What does ^M character mean in Vim?
Unix uses 0xA for a newline character. Windows uses a combination of two characters: 0xD 0xA. 0xD is the carriage return character. ^M happens to be the way vim displays 0xD (0x0D = 13, M is the 13th letter in the English alphabet).
You can remove all the ^M characters by running the following:
:%s/^M//gWhere ^M is entered by holding down Ctrl and typing v followed by m, and then releasing Ctrl. This is sometimes abbreviated as ^V^M, but note that you must enter it as described in the previous sentence, rather than typing it out literally.
This expression will replace all occurrences of ^M with the empty string (i.e. nothing). I use this to get rid of ^M in files copied from Windows to Unix (Solaris, Linux, OSX).