I do not understand the difference between conversation (n) and talk (n). I am only interested in the difference in the following definitions:

• conversation (n):
  an informal talk involving two people or a small group of people : the act of talking in an informal way
• talk (n):
  -an occurrence in which one person talks about something with another person : a conversation or discussion or
  -the act of talking about a subject with another person or group : discussion or conversation