steady job; regular employment; occupation
Refers to a stable, long-term job or one's regular field of work. Often used in contexts of employment status, such as 定職に就く (to find steady work) or 定職がない (without a regular job).
He hasn't found a steady job yet.
If you have regular employment, your life becomes stable.
Compound of 定 (てい, 'fixed, steady') and 職 (しょく, 'job, employment'). The meaning is transparent from its components.