An expression is a maths sentence made up of terms which can have numbers and or variables as factors.
#3x," "3x+5," "2x^2-5x+3# are all examples of expressions.
An equation is a statement that two expressions are equal, so we have:
#"expression = expression"#
An equation is solved, which means to find the value(s) of the variable(s) which makes the equation true,
#3x-5 = 22" "rarr x = 9#
#x^2 +4x -45 =0" "x = -9 or x=5#
An equation which contains two or more variables does not have a unique solution, but rather many, many solutions,
#x+y=10 # has infinitely many solutions.