What is index sequential search?

Excuse me, could you please elaborate on what exactly is meant by "index sequential search"? I'm a bit confused about the terminology. Is it a specific type of algorithm or method used in data structures and algorithms? If so, how does it differ from other search techniques? I'm particularly interested in understanding its application in the field of cryptocurrency and finance, if any. Additionally, could you provide a brief overview of how it works and its advantages or disadvantages? Thank you in advance for your clarification.