It is like a spreadsheet with hugh limitless rows and columns, each rows will be identified by key. It is different from traditional Hierarchy Database where it will have lot of tables and each table will be linked by keys. BigTable will have only one table with limitless rows and columns. We can perform joins, sub selects and other queries in bigtable similar to Traditional hierarchial tables, but in a different way.
Many projects at Google store data in Bigtable, including web indexing, Google Earth, and Google Finance.Bigtable has successfully provided a flexible, high-performance solution for all of these Google products.