WHAT ARE GOOD ENTRIES AND EXITS?

Given a mechanical trading system that contains an entry model to generate entry orders and an exit model to generate exit orders (including those required for money management), how are the entries and exits evaluated to determine whether they are good?
In other words, what constitutes a good entry or exit?
Notice we used the terms entry orders and exit orders, not entry or exit signals.
Why?
Because “signals” are too ambiguous.
Does a buy “signal” mean that
one should buy at the open of the next bar, or buy using a stop or limit order? And
if so, at what price? In response to a “signal” to exit a long position, does the exit occur at the close, on a profit target, or perhaps on a money management stop?
Each of these orders will have different consequences in terms of the results achieved.