tab

1 tab /ˈtæb/ noun
plural tabs
1 tab
/ˈtæb/
noun
plural tabs
Britannica Dictionary definition of TAB
[count]
1 
a  : a small, flat piece on a box, envelope, etc., that can be put into a hole in order to hold two parts together
b  : a small, flat piece that sticks out from the edge of something (such as a folder) and allows you to identify and find it easily
c  US : a small piece of metal, plastic, etc., that is pulled in order to open or close something
2 
US, informal : a record of the things (such as drinks at a bar) that a customer has ordered and will pay for later
3 
: tab key
4 
informal : a small pill of an illegal drug

keep tabs on

informal
: to carefully watch (someone or something) in order to learn what that person or thing is doing
2 tab /ˈtæb/ verb
tabs; tabbed; tabbing
2 tab
/ˈtæb/
verb
tabs; tabbed; tabbing
Britannica Dictionary definition of TAB
1 
[+ object] : to put a small, identifying label (called a tab) on something — often used as (be) tabbed
2 
[+ object] US, informal : to say that (someone or something) will do something or have a particular role or purpose — often used as (be) tabbed
3 
[no object] : to hit the tab key on a computer or typewriter