A CTF (Capture The Flag) is a information security competition that challenges contestants to solve a variety of tasks ranging from exploiting a web page, to decrypting audio steganography, to hacking your way into a server to steal data.
Jeopardy-style CTFs have questions (tasks) in range of categories. For example, these categories may include : forensics, cryptography, binary exploitation, web exploitation, and reverse engineering. Teams can gain points for every solved task. Usually, more points will be given for completing more complicated tasks. In certain CTFs, the next task in a task chain can be opened only after a team solves the previous task.
Tasks are similar to puzzles. Each task has a certain “flag” or solution (usually in the form of a readable message) that teams have to find.