ARM is an adjustable-rate mortgage that has an initial (fixed) interest rate for the first period of time and thereafter adjusts each year. Each annual rate adjustment is based on another rate - often the yield on a Treasury note.   
       
Fixed rate mortgage is a loan that has an interest rate that stays the same for the whole term of loan. The principal amount is reduced, slowly at first, and then at an accelerating pace, over the life of the loan.

Jumbo mortgage is a home loan that exceeds the limits set by Fannie Mae and Freddie Mac (the 2006 limit is $417,000; $625,500 in Alaska, Hawaii and the U.S. Virgin Islands). Jumbo mortgages generally have a slightly higher interest rate than smaller (sometimes called "conventional" or "conforming") mortgages.

Here are some examples:
1-year ARM is a 30-year loan in which the rate (and therefore your monthly payment) changes every 12 months
3-year ARM is a 30-year loan in which the rate (and therefore your monthly payment) changes every 36 months
3/1 ARM has an initial interest rate for the first three years and thereafter adjusts each year
5/1 ARM similarly has a fixed interest rate for the first five years and thereafter adjusts yearly
3/27 ARM has a fixed rate for the first three years and then adjusts for each of the next 27 years
30-year fixed mortgage is a loan that has an interest rate that stays the same for the 30-year term of the loan
5/1 jumbo is an ARM that exceeds a certain amount, it has a fixed rate for the first three years and then adjusts yearly based on index