1. Limitation on Elective Deferrals ( $17,000 for 2012):
this is for defered tax purpose.
2. Max annual contributions (the lesser of 100% of your compensation or $50,000 for 2012).
At least for our company, it would keep matching your contribution even after the $17,000 limitation, but would stop matching after you reach your max annual contribution.
Link for the two terms defined by IRS:
http://www.irs.gov/retirement/participant/article/0,,id=151786,00.html