A crawler is a programme that visits web sites and reads their pages and other information in order to create entries for a search engine index. The major search engines on the web all have such a programme, which is also known as a ‘spider’ or a ‘bot’. Source: http://searchsoa.techtarget.com/definition/crawler; cited by EU OD

When extracting data from the web, the term ‘crawling’ is often also referred to as ‘data scraping’ or ‘harvesting’. There is a difference between these terms: crawling refers to dealing with large datasets where one can develop his or her own crawlers (or bots), which crawl to the deepest parts of the web pages. Data scraping, on the other hand, refers to retrieving information from any source (not necessarily the Web). Source: https://www.promptcloud.com/blog/data-scraping-vs-data-crawling/; cited by EU OD