Any protocol or user can attach bribes onto a liquidity pool and those who vote for it will be able to claim them.
Plenty natively supports gauge bribes and automatically adjusts them according to weekly vePLY NFT votes. In addition to traditional bribes, which allows a protocol to expand their on-chain liquidity by bribing vote escrow holders to vote in a specific way (e.g. Convex bribing veCRV token holders). Plenty allows any user to attach bribes onto a gauge.
The concept of bribes was made popular by Convex which came to control a large share of Curve voting power. As users kept chasing high CRV rewards, protocols realized they could grow their protocol and on-chain liquidity by bribing veCRV holders to vote for their pool.
On Plenty, it’s possible for anyone to attach bribes onto a gauge and those who vote for it are then able to claim them.
Who can bribe?
Anyone can issue a bribe to attract voters to a specified gauge in a specified epoch. However, bribers would most likely be:
Protocol owners who are aiming to bootstrap liquidity for their protocol's token.
Liquidity providers who have high stakes in a certain pool.
Bribes must be given in fungible tokens. A bribe given in NFTs won't be divisible amongst the voters. Moreover, really small bribes especially in low-precision tokens should be avoided.