What exactly is A dataset? is a database contain more than 2 tables counted as 1 or 2 datasets?
A dataset might refer to any collection of information about a specific topic. Namely, a file, an excel file, a .txt file, etc.

Usually, we use datasets that are saved in a table format (like .csv files) 
a dataset in this form is exactly like a table having columns (fields) for the name of its features and rows that are the records (samples) and an index for each row.
A problem might be solved using multiple datasets (tables) but each dataset is referred to a single table (data frame)

Whatever the format is, for utilizing, we turn the dataset to a table (dataframe)