Used for a person or thing that serves as a replacement or backup, often in sports, work, or equipment contexts.
Prefix used in compounds to indicate something secondary, auxiliary, or subordinate, such as サブリーダー (sub-leader) or サブタイトル (subtitle).
He's serving as a backup for the team this season.
He sat on the bench as a substitute for the match.
You'd better bring a backup battery.
In this project, I supported the team as a sub-leader.
Because of an injury, he was moved to the backup lineup.
The coach used the young player as a substitute.
レギュラー is the regular, first-string member or item, the direct opposite of サブ meaning a backup or reserve.
As a prefix, メイン- marks the main or primary thing in a compound, opposite to サブ- which marks something secondary or auxiliary.
Loanword from English 'sub', a clipping of 'substitute' or 'sub-'. Entered Japanese in the 20th century and is now common in sports, business, and technology contexts.
sub-goal; intermediate goal
sub-site; subsite
small knapsack
subshell
subset
subtype