Sometimes (often?) logic probes have a pulse/memory feature that can be used to show a rapid pulsing signal you are probing as a slow pulsing LED. An example would be a multi MHz clock line for a microprocessor. But if you are looking for a single pulse or level transition then you set it to Memory so that the LED stays lit so you won't miss it.
Just a quick look on Ebay shows the not surprising confusion due no doubt to language.
You are expected to have a pulser AND a probe as you realise.