If you're working in Vim and paste something into the terminal, sometimes you'll get a "staircase" effect where each line is progressively spaced farther outward, like so:
line 1
line 2
line 3
line 4
Obviously, this isn't usually desirable.
To correct this, you can enable paste to prevent the staircase effect. In command mode, type:
:set paste
This isn't on by default. When paste is enabled, it disables mapping and some other functions, so you probably want to know how to turn it off as well:
:set nopaste
Happy vimming!
Reference: http://www.dissociatedpress.net/2009/12/22/vim-tip-using-paste-to-avoid-the-staircase-effect/