Terms of study in US universities

US institutions typically follow a semester system or a quarter system.

Semester system:

A semester system typically involves three 15-week terms of study :

• Fall : Typically August to November end
• Spring: January to May
• Summer: May to August (typically shorter)

Quarter system:

A quarter system typically involves four 10-week terms of study:

• Winter: Typically January to March
• Spring:  April to June
• Summer: June to August 
• Fall: September to December

Both systems have their own pros and cons. All universities follow either of the systems. 

Difference between M.S & M.Eng?

M.S is the abbreviation of Master of Science and M.Eng is the abbreviation of Master of Engineering. 

Some universities offer M.S while others offer M.Eng. Both are master's course and can be used to enhance the boundaries of one's knowledge in a field. M.S is more of a research oriented course while M.Eng has more of a course-work based curriculum. Finally, it is up to an individual to decide whether he would like to do a M.S or M.Eng degree.

Note: Some universities offer S.M degree instead of M.S (Both are basically the same!).