digging in; cutting into
Physical sense of something pressing or cutting into a surface or skin, such as a rope, strap, or tight clothing.
The backpack strap digs into my shoulder and hurts.
This underwear has less digging in and is comfortable.
inroads; encroachment; eating into
Figurative use for making gradual gains into a market, territory, or support base, often at the expense of a competitor.
The new product is making inroads into the rival company's market share.
The opposition party is trying to eat into the ruling party's electoral base.
Used in financial or accounting contexts to describe a shortfall or negative balance, often as part of compound terms like 赤字食い込み.
We cut expenses to prevent a budget deficit.
wedgie
Colloquial term for when underwear rides up between the buttocks; often used in casual or humorous contexts.
I can't concentrate because my underwear is giving me a wedgie.
Noun form of the verb 食い込む (くいこむ), from 食う (eat) + 込む (go into). The figurative senses developed from the physical idea of something biting or cutting into something else.