Rikki ... "Stop time", as I learned the phrase, is used at some point in a tune to feature on of the instruments, or vocal ... In the most simple style, all of the instrumentalists would hit the appropriate chord on the 1 beat of the measure and then stop while the soloist played for the rest of the measure ... this would be repeated for as many measures as desired .... in a I- IV- I- V- I- blues tune (depending upon the chord pattern) it is often played for the I chord and the soloist plays the "fill" part until the IV chord, when the whole group plays again ...
Another simple example might be the bridge to "Route 66" where the whole group would hit the chord on the lyrics in caps, while the vocalist would sing the remaining lyrics with no accompaniment....
"you can GO to st. louis, JOPlin missouri, OKlahoma city is mighty pretty ... etc.
I don't know if that clears it up any for you, it's kind of difficult for me to explain verbally ... Perhaps some of the more accomplished musicians can help with an explanation ...
t.