What is the meaning of probabilistic polynomial time adversary? I learned about probabilistic polynomial time adversary, but I have some doubt. 


Is probabilistic polynomial time adversary referred to those who attack in polynomial time with the form of probabilistic?
Yes, but note as below, the probability is not biased.
From the Lindell, Katz book;

An algorithm $A$ is said to run in polynomial time if there exists a polynomial $p(\cdot)$  such that for every input $x \in \{0,1\}^*$, the computation of $A(x)$ terminates within at most $p(|x|)$ steps.
A probabilistic algorithm is one that has the capability of &quot;tossing
coins&quot;, i.e. the algorithm has access to a random source of randomness
that yields unbiased random bits that are independently equal to 1
with $1/2$ probability and to 0 with $1/2$ probability.

Probabilistic Polynomial-time adversary means; An adversary runs in probabilistic polynomial time algorithm.

Different formulation (due to a comment of SEJPM):

A probabilistic polynomial-time algorithm is a probabilistic algorithm that may only perform a polynomial amount of operations including at most a polynomial number of coin-flips.
A probabilistic polynomial-time adversary is then any probabilistic polynomial-time algorithm.