Meaning of “default” - Learner’s Dictionary

default

noun uk us /dɪˈfɔːlt/

[ no plural ] what exists or happens usually if no changes are made

by default

If something happens by default, it happens only because something else does not happen:

No one else stood in the election, so he won by default.
default adjective [ always before noun ]

The default font size is 10.

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