Map lets you process each line from stdin with a command of your choice. For example:

Note that the command must be wrapped in single quotes to prevent the variable from being expanded by the shell.
There are many ways to accomplish what you can do with map, including find, xargs, awk, and shell for-loops. The approach taken by map is extremely pragmatic and allows me to express concisely what I want. Given the fact that it's designed as a filter, it can operate on any kind of list, not only lists of files.

The problem that prompted me to think about map was the following: given a list of files, I wanted to execute two commands on each. Here's how you can do it with different tools: