specialism

Concentration of one’s efforts in a given occupation or field of study.

A field of specialization.

Devotion to a special branch or division of a general subject or pursuit; the characteristic pursuit or theme of a specialist; restriction to a specialty.

Devotion to a particular and restricted part or branch of knowledge, art, or science.

speciality

The concentration of one’s efforts upon a particular field of study

the special line of work you have adopted as your career

the concentration of your efforts on a particular field of study or occupation