Mls
In short
Major League Soccer is the top professional men's football league in the United States and Canada. It currently consists of 30 teams competing across North America.
In plain words
It is the highest level of professional football in North America. Most teams are based in the USA, but three teams play in Canada. The league is run from New York City.
A simple example
A fan in Los Angeles might go to a stadium to watch Los Angeles FC play against a visiting team from Toronto.
Why it matters
It is the primary platform for professional football talent in North America. The league helps grow the popularity of the sport in the United States and Canada.
Easy to mix up
Do not confuse it with the USL, which is a lower tier of professional football in the same region.