Perpetual Protocol is an AMM-based DEX, making trading somewhat different from the traditional order book exchange model seen in traditional finance and early Ethereum DEXs.
Makers and Takers
Every trade is made with the Perpetual Protocol vAMM as the maker. However, there are no additional fees for trading as a taker.
This is one of the nice features about the vAMM model (and what makes our limit orders different to orders on other sites). If you place a limit order to buy 1 ETH at $2000, then you will be the taker and the vAMM will be the maker.
Functionally, with a vAMM a limit order to buy 1 ETH at $2000 is the same as saying "Place a market order for 1 ETH only when the price is below $2000." So it is quite likely that you actually get a better price than your order asked for.
If ETH drops from $2001 to $1950 suddenly (ie. in 1 block), then Apex will execute your order at the current price of $1950.