Plain English Meaning
Strobes are fake streaks on a weather radar picture that look like they shoot outward from the radar location. They are not real weather — the radar is picking up something other than rain or snow and drawing it on the map.
Full Definition
In NEXRAD weather radar imagery, strobes are false radial lines or spikes that appear to extend outward from a radar site, caused by the radar antenna detecting non-weather sources of radio energy such as the sun, wind farms, or other transmitters. They are a known display artifact and do not represent actual precipitation.
Context Anchor
Seen when interpreting NEXRAD weather images and checking whether displayed returns are real weather or radar abnormalities.
Derivation
From the Greek strobos, meaning 'a whirling' or 'spinning.' The term carries over to radar because these false returns appear as straight lines radiating outward, like spokes from a spinning wheel on the radar site.