Simple Definition:

A career is a person’s chosen profession or occupation [the job that they do to earn a living]. It refers to the series of jobs or positions that a person holds throughout their working life [the time when they are employed].

For example:

• A doctor is someone who has chosen a career in medicine (the field of medicine).
• A teacher is someone who has chosen a career in education (the field of teaching).

Very Simple Definition:

A career is the job or work that someone does. It is the job that they choose to do for a long time.

For example:

• He hopes to have a long career as adoctor (to work as a doctor for a long time).
• Some people choose teaching (being a teacher) as their career.