What does "gain ground" mean?

Advance, make progress; also, win acceptance. For example, The new conservation policy is gaining ground among the voters. This expression alludes to a military advance in which an army literally takes territory from the enemy. Its figurative use dates from about 1800. For an antonym, see lose ground.

gain ground on or upon. Encroach on, advance at the expense of. For example, Door-to-door canvassing helped them gain ground on the opposition.