Terms are made up of letters or numbers or a mixture of both.
An expression is made up of terms added together, such as 4m - 5 + 6d2 which is made up of 3 terms
Coefficients are simply the numbers which appear before letters in an algebraic term.
The coefficient of 3m is 3
The coefficient of -5d is -5
The coefficient of -2d3 is -2