The original meaning for "staking" is that, for PoS networks, you put some coins, say ETH, to run a network validator, who secure the network by producing valid blocks, and in return you get a profit in that same coin (the network prints coins at a fixed rate per year, say 10% ETH, to attract validators). The coins are needed to prevent sybil attacks (i.e. preventing someone to running infinite validators and attack the network). So if you own 1% coin you can only run 1% validator and won't be able to flood the network.
However running a validator is hard, requires custom servers and hardware, so people simply delegate them to another validator, who does the validation on their behalf and distributes the reward to its delegators. In essense, you earn 10% ETH simply by voting a validator. Note that this IS safe and in most cases, people do get their coins and profits back and it's very secure. You can't lose money in the sense that you won't lose ETH. There are ill-minded people to steal people's funds, but that's not the general case.
Since most people only cared about the profit part, the term "staking" has since changed meaning to become anything that requires you to put coins in and get coins back. Staking UST is one case: you lend UST to the protocol and withdraw UST at any time, and the protocol prints you UST at 20% APR. There are lending protocols, airdrops requiring you to stake something, providing liquidity to collect fees, etc. And for simplicity they all become "staking".
Note that while staking is secure, it doesn't change the argument about how ETH is just junk bonds. If they offer 3% return per year, it's essentially printed money and the currency's value would decline 3% per year as well. If they lock you in for a longer period (ETH staking locks you in indefinitely until The Merge goes live for half a year), you are kept from selling your ETH and these coins are already worthless once they are unlocked. Buying ETH for staking is essentially providing liquidity for people selling ETH so they can make a quick profit.