An xlsx file extension stands for an Excel spreadsheet file.
An Excel spreadsheet is a type of spreadsheet file format. It is the default file format for Microsoft Excel and other spreadsheet applications.
An Excel spreadsheet consists of rows and columns of data, where each column contains some number of values, typically in numerical order. A single cell can contain text as well as other data types such as dates or formulas that return a value.
An HTML table is a type of web markup used for displaying tabular data on web pages. Tables are made up of rows and columns, which may be nested within other tables. Cells contain information in an ordered format that can be displayed as text or numbers depending on the type of cell (text cells often have text values, whereas numerical cells contain numerical values).