"Stop-time" blues is the blues where, as in this example, after playing the basic riff, you stop to insert a lyric line (or a cool guitar or harmonica fill). There's a million blues songs that use this.
The below example is one that is commonly used, shown here in the key of E. All you really need to do is alternate between the E and A chords at the beginning of each measure.
The blank space after the main riff can be filled with neat little licks or with the vocal line. To keep it simple, I've filled the blanks here with a little strumming across muted strings or with part of an E7 chord.
Stop-time stuff can be used in various ways. This example is one that I use to play "Mannish Boy," and it just repeats the same riff over and over again. Check out the next page for my "Hoochie Coochie Man" example, which integrates the stop-time with a blues shuffle (note that these are not note for note transcriptions from Muddy, 'cause I only play acoustic
). On page 3 is an example which uses a 12-bar stop-time pattern, page 4 shows how you can stick a stop-time riff into a normal 12-bar blues progression.