What does mean “Transfer Tax”
On some tokens, each transfer(transaction) can cost you a transfer tax of up to 5% (!).
A part of these transfer tax are possibly added to the liquidity pool, are burnt or going to the treasury.
This rate is fixed in the token contract, so whatever AMM/DEX you use the transfer tax will be deducted (on some contracts the transfer tax % value can be updated)
These transfer taxes can cause troubles, such as for example forcing the user to increase the slippage tolerance on PancakeSwap or other AMM/DEX.