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What is 2 and explain in detail?
2 (two) is a number, numeral and digit. It is the natural number following 1 and preceding 3. It is the smallest and only even prime number. Because it forms the basis of a duality, it has religious and spiritual significance in many cultures.

Evolution
Arabic digit
The digit used in the modern Western world to represent the number 2 traces its roots back to the Indic Brahmic script, where "2" was written as two horizontal lines. The modern Chinese and Japanese languages (and Korean Hanja) still use this method. The Gupta script rotated the two lines 45 degrees, making them diagonal. The top line was sometimes also shortened and had its bottom end curve towards the center of the bottom line. In the Nagari script, the top line was written more like a curve connecting to the bottom line. In the Arabic Ghubar writing, the bottom line was completely vertical, and the digit looked like a dotless closing question mark. Restoring the bottom line to its original horizontal position, but keeping the top line as a curve that connects to the bottom line leads to our modern digit.In fonts with text figures, digit 2 usually is of x-height, for example, .

Etymology of two
The word two is derived from the Old English words twā (feminine), tū (neuter), and twēġen (masculine, which survives today in the form twain).The pronunciation /tuː/, like that of who is due to the labialization of the vowel by the w (combare from womb), which then disappeared before the related sound. The successive stages of pronunciation for the Old English twā would thus be /twɑː/, /twɔː/, /twoː/, /twuː/, and finally /tuː/.

In mathematics
Two is the smallest prime number, and the only even prime number, and for this reason it is sometimes called "the oddest prime". As the smallest prime number, it is also the smallest non-zero pronic number, and the only pronic prime. The next prime is three, which makes two and three the only two consecutive prime numbers. Two is the first prime number that does not have a proper twin prime with a difference two, while three is the first such prime number to have a twin prime. In consequence, the first pair of twin primes, three and five, encase four in-between, which is the square of two, or 
  
    
      
        
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    {\displaystyle 2^{2}}
  . Two is the first Sophie Germain prime, the first factorial prime, the first Lucas prime, and the first Ramanujan prime. It is also a Motzkin number,  a Bell number, an all-Harshad number, a meandric number, a semi-meandric number, an open meandric number, and the third (or fourth) Fibonacci number.An integer is called even if it is divisible by 2. For integers written in a numeral system based on an even number such as decimal, divisibility by 2 is easily tested by merely looking at the last digit. If it is even, then the whole number is even. In particular, when written in the decimal system, all multiples of 2 will end in 0, 2, 4, 6, or 8.Two is the base of the binary system, the numeral system with the fewest tokens that allows denoting a natural number n substantially more concisely (with log2 n  tokens) than a direct representation by the corresponding count of a single token (with n tokens). This binary number system is used extensively in computing.
For any number x:

x + x = 2 · x addition to multiplication
x · x = x2 multiplication to exponentiation
xx = x↑↑2 exponentiation to tetrationExtending this sequence of operations by introducing the notion of hyperoperations, here denoted by "hyper(a,b,c)" with a and c being the first and second operand, and b being the level in the above sketched sequence of operations, the following holds in general:

hyper(x,n,x) = hyper(x,(n + 1),2).Two has therefore the unique property that 2 + 2 = 2 · 2 = 22 = 2↑↑2 = 2↑↑↑2 = ..., disregarding the level of the hyperoperation, here denoted by Knuths up-arrow notation. The number of up-arrows refers to the level of the hyperoperation.
Two is the only number x such that the sum of the reciprocals of the natural powers of x equals itself. In symbols,

  
    
      
        
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    {\displaystyle \sum _{k=0}^{\infty }{\frac {1}{2^{k}}}=1+{\frac {1}{2}}+{\frac {1}{4}}+{\frac {1}{8}}+{\frac {1}{16}}+\cdots =2.}
  This comes from the fact that:

  
    
      
        
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    {\displaystyle \sum _{k=0}^{\infty }{\frac {1}{n^{k}}}=1+{\frac {1}{n-1}}\quad {\mbox{for all}}\quad n\in \mathbb {R} >1.}
  A Cantor space is a topological space 
  
    
      
        
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    {\displaystyle 2^{\mathbb {N} }}
   homeomorphic to the Cantor set. The countably infinite product topology of the simplest discrete two-point space, {0, 1}, is the traditional elementary example.  
The sum of the reciprocals of all non-zero triangular numbers converges to 
  
    
      
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    {\displaystyle 2}
  .Powers of two are central to the concept of Mersenne primes, and important to computer science. Two is the first Mersenne prime exponent.
Taking the square root of a number is such a common mathematical operation, that the spot on the root sign where the index would normally be written for cubic and other roots, may simply be left blank for square roots, as it is tacitly understood.
The square root of 2 was the first known irrational number.
The smallest field has two elements.
In a set-theoretical construction of the natural numbers, 2 is identified with the set {{∅},∅}. This latter set is important in category theory: it is a subobject classifier in the category of sets.
Two consecutive twos (as in "22" for "two twos"), or equivalently "2-2", is the only fixed point of John Conways look-and-say function