Hi Deepika,

A lecturer is the tile of a teacher who has just started to teach at college and university level in undergraduate courses. These are academics at an early stage of their careers and can teach part time or full time in colleges and universities. Lecturers are teachers who also assist research students in their endeavors and do not have tenures. 

A professor is a senior academic who has many years of teaching experience. What makes him different is not just his seniority but the fact that he has carried out research in his chosen field of study and earned the degree of a doctorate. After doing Ph.D., a lecture becomes an assistant professor which is the starting rank in the teaching profession, but the assistant professor does not have tenure. Tenure means a permanent position and assistant professor with tenure cannot be easily dismissed. Assistant professors teach for 5-7 years, to get tenure, but if rejected, they have a chance to get tenure from another college or university within a year. 

Good Luck!