What is Indexing?
Indexing is a process when a certain webpage is found by crawlers and the content of the webpage is rendered. Key signals are noticed and all data is tracked in the index. The index is a database created by the search engine. There are stored all data on every website, that was found by search engine.
After indexing website is indexed. It means, that site was processed and it will be shown in search engine's search results. If the website is not indexed, users are not able to find it.