A fixed interest rate loan is a loan where the interest rate doesn't fluctuate during the fixed rate period of the loan. This allows the borrower to accurately predict their future payments. Variable rate loans, by contrast, are anchored to the prevailing discount rate.
Conventional loans typically are harder to qualify for than FHA loans and require a slightly higher down payment. However, in some cases rates can be lower and have lower closing costs. Also, monthly mortgage insurance is usually less or can be nothing with 20% down payment.