What does "by and large" mean?

Mostly; generally; all things considered.

By and large

Common synonyms include: all in all, all things considered, almost entirely, altogether, approximately, as a rule.

adv

adv ·Rare ·Advanced level

Adverb

1
Mostly; generally; all things considered. focus, idiomatic, not-comparable
"It was, by and large, an unexceptional presentation."
2
In one way or another. idiomatic, not-comparable, obsolete
"Miss Betsey, a charming frigate, that will do honour to our country, if you take her by and large."
3
Sailing alternately into the wind and in the same direction as the wind. not-comparable
"[…] For to make a Ship to drawe or goe but little into the water, and to hold a good winde, and to ſaile well both by and large, were very neceſſarie, and eſpecially in theſe our ſhallowe Seas, […]"

Adverb

"It was, by and large, an unexceptional presentation."

From sailing: a ship may (or may not) sail well both close by the wind, and large, downwind, with sheets extended.