I'm from a non-technical background. (Mentioning this for the convenience of explanation w.r.t intelligibility)
Book Name - "Introduction to Algorithms"
Authors - Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein.
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Sign up to join this communitySingle means that they are talking about only one computer. Sequential means that they are not considering computers that can execute multiple instructions in parallel (as an example think of computers with multiple processors or processor cores).