Meaning of “subject” - Learner’s Dictionary

subject

noun [ C ] uk us /ˈsʌbdʒɪkt/
WHAT

B1 what someone is writing or talking about:

a series of programmes on the subject of homelessness
STUDY

A1 an area of knowledge studied in school or university:

Chemistry is my favourite subject.
GRAMMAR

B1 the person or thing that performs the action described by the verb. In the sentence 'Bob phoned me yesterday.', 'Bob' is the subject.

PERSON

someone who is from a particular country, especially a country with a king or queen:

a British subject

(Definition of “subject noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)