What is a t slot and its purpose?

In notebooks , Small outline Dual Input Memory Module slots are used since there is lack of space in smaller and compact devices SO-

See here, the meanings of the word slot, as video and text slot (noun

what does slot mean in football What is SLOTS meaning?

what is a quick pick lottery ticket A thin opening or groove in something is a slot You can put letters and postcards through the mail slot at the post office