alright noted, I usually think both are the same as they can be used interchangeably

When Search engine read your site link that is Crawling and when search engine approved tour link in search status that called Indexing.

Crawling means collecting all data from your website.
Indexing is to store that data in their database for the particular search term or query.

Crawling means the search engine robot crawl or fetch the web pages while Indexing means search engine robot crawl the web pages, saved the information and it appear in the search engine.