The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is "ρ" (the lower case Greek letter rho), although the Latin letter "D" can also be used. Mathematically, density is defined as mass divided by volume: 

where "ρ" is the density, "m" is the mass, and "V" is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight. 

For a pure substance the density has the same numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. 

To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material, usually water. Thus a relative density less than one means that the substance floats in water. QUESTIONS:

Q1:
1. Is there one strict definition of density?
2. Does everything define density in the same way?
3. Is density always defined in the same manner in all context?
Q2:
1. What elements are the most dense at regular conditions?
2. Under regular conditions, which elements are the densest?
3. What two elements are the most dense with conditions that are regular?
Q3:
1. How is a substance's density determine?
2. How do you find the density of a substance?
3. What is the density of a substance defined by?
Q4:
1. How is substance mathematically defined?
2. What is the mathematical definition of density?
3. How is substance calculated in mathematics?
Q5:
1. What does V stand for in density equations?
2. In the equation to determine density, what does V mean?
3. What does the V represent when determining density?
Q6:
1. What does P stand for in density equations?
2. In the equation to determine density, what does P mean?
3. What does the P represent when determining density?
Q7:
1. What does M stand for in density equations?
2. In the equation to determine density, what does M mean?
3. What does the M represent when determining density?
Q8:
1. Is the English langauge letter P used in the density equation?
2. Does the density equation have the letter P from the English alphabet in it?
3. Does the density equation use the letter P from the English alphabet?
Q9:
1. What language does the P in the density equation come from?
2. What language is used for the letter P in the desnity equation?
3. When determining density, the letter P from what language is used?
Q10:
1. What letter resembles a P in the Greek alphabet?
2. Which Greek letter looks like a P?
3. Which letter in the Greek alphabet looks similar to a P?
Q11:
1. What symbol, other than rho, is used for density?
2. What's the symbol besides rho that can be used for density?
3. What symbol can represent density, in addition to the letter rho?
Q12:
1. In what context is density defined as weight per unit volume?
2. Who defines density as weight per unit volume?
3. In what context is density calculated as weight per unit volume?
Q13:
1. Is the United States oil and gas industry's definition of density correct?
2. Does the United States oil and gas industry use an accurate definition of density?
3. Is it accurate to define density as weight per unit volume?
Q14:
1. Is the United States oil and gas industry's definition of density scientifically accurate?
2. Would a scientist define density as weight per unit volume?
3. Is density defined as weight per unit volume in scientific contexts?
Q15:
1. What definition of density is better than that of the United States oil and gas industry?
2. How can we define density better than the United States oil and gas industry does?
3. What is a more accurate definition of density than weight per unit volume?
Q16:
1. In what context is density the same value as its mass concentration?
2. When does density become the same value as its mass concentration?
3. 
Q17:
1. What is a replacement for density when trying to make comparison easier?
2. For more simple comparisons, what stands in for density?
3. What is used in place of density for more simple comparisons?
Q18:
1. What's an example of a dimensionless quantity?
2. What is one instance of a dimensionless quantity?
3. Give an example of a dimensionless quantity.
Q19:
1. What's an example of a dimensionless quantity, that is not relative density?
2. What is one instance of a dimensionless quantity, other than relative density?
3. Give an example of a dimensionless quantity, besides relative density.
Q20:
1. What is the relative density of floating objects?
2. What relative density do floating objects have?
3. What is the relative density of a floating object calculated as?
