Subject.
The person, or place, or thing, or state which is spoken of is called the Subject.
I forgot my umbrella.
Anuradhapura is a historical city.
Gold is a precious metal.
Forgetfulness is a bad habit.
Here I, Anuradhapura, Gold and Forgetfulness are the Subjects of the sentences.
Singular Subjects.
They are: I (am), You (are), He (is), She (is), It (is) and A name or A place or A thing or A state/condition [(is) standing as Subject/s].
Plural Subjects.
They are: We (are), You (are), They (are) and Names or Places or Things or States/Conditions [(are) standing as Subject/s].