Explain Spiders, Robots, and Crawlers?

Hi Friends,
These terms can be used interchangeably - essentially computer programs that are used to fetch data from the web in an automated manner. They also must follow the directives mentioned in the robots.txt file present in the root directory.

A Web crawler, sometimes called a spider or spiderbot and often shortened to crawler, is an Internet bot that systematically browses the World Wide Web, typically for the purpose of Web indexing (web spidering).

Web search engines and some other sites use Web crawling or spidering software to update their web content or indices of others sites' web content. Web crawlers copy pages for processing by a search engine which indexes the downloaded pages so users can search more efficiently.

They are all the same and search engine automated programs that are responsible to read through webpages sources and provide information to search engines.

As per my opinion spider / robots and crawlers all are same. they work for the same purpose means collecting content and sending for indexing.