Explain front end and back end in brief -

The phases are collected into a front end and back end

The front end consist of those phases, that depends primarily on source language and largely independent of the target machine
Front end includes lexical analysis, syntax analysis, semantic analysis, intermediate code generation and creation of symbol table
Certain amount of code optimization can be done by front end

The back end consists of those phases, that depends on target machine and do not depend on source program
Back end includes code optimization and code generation phase with necessary error handling and symbol table operation