You're looking at output redirection (Bash). 2 stands for 'stderr', the error output. By redirecting it to
/dev/null, you're discarding it to oblivion. Regular output, 'stdout' or 1 is still shown (in your terminal by default), though.
Basically, this is just silencing error output of the
A snippet from the above link explains it more general:
# Redirect stdout to a file.
# Creates the file if not present, otherwise overwrites it.
ls -lR > dir-tree.list
# Creates a file containing a listing of the directory tree.
# Redirect stdout to file "filename."
# Redirect and append stdout to file "filename."
# Redirect stderr to file "filename."
# Redirect and append stderr to file "filename."
# Redirect both stdout and stderr to file "filename."