What is a strobed input in microprocessor?

A strobe is a signal that defines a sampling period for another signal. Strobes are usually level sensitive. For example, an analog-to-digital converter often has a sample-hold circuit in front of it controlled by a strobe: "on" means sample, "off" means hold.

In signal processing the strobe-open time is called the "aperture". The fact that it is non-zero in real systems leads to an artifact called "aperture error".

A clock by contrast is edge-sensitive. Clocks too can have a kind of aperture error - jitter - which also causes artifacts in processing.