A lockpick is a small tool, or set of tools designed to aid in the art of picking locks
The MIT Guide to Lockpicking is the best reference available on this subject. However another guide is
Anarchist's Cookbook: The Arts of Lockpicking I and
Anarchist's Cookbook: The Arts of Lockpicking II
However, breifly a lockpick is usualy a thin metal tool with a certain tip at the end.
The tip can be a triangle, a diamond, or circle, either half or full.
The pick is designed to manipulate the pins inside the tumbler of a key lock in order to fool the lock into thinking the correct key has been inserted and thus allowing the tumbler to be turned, and the lock opened.
Please note, these tools maybe considered a tool to facilitate breaking and entering and therefore maybe illegal in certain countries and states unless you have a good reason for being in posession of such tools (Eg you are a locksmith).