Indexing is how Magento2 transforms data such as products, categories, and so on, to improve the performance of your storefront. As data changes, the transformed data must be updated—or reindexed. Magento2 has a very sophisticated architecture that stores lots of merchant data (including catalog data, prices, users, stores, and so on) in many database tables. To optimize store front performance, Magento2 accumulates data into special tables using indexers.
In Magento2, there is none interface from admin, to re-index manually at a time as we did in magento1, for doing this we need to use
terminal. Using Terminal we can did full indexing of magento2, whenever we need, to do this we just only need to open terminal and reach the root directory of magento2 installation and type below mentioned command.
magento indexer:reindex [indexer]
[indexer] is a space-separated list of indexers. Omit
[indexer] to reindex all indexers.