Google Trends is a free tool that analyses the popularity of search queries across various regions and languages. It provides insights into search trends over time, which can be invaluable for performing keyword research, understanding search intent and generating topic ideas. You can type in a keyword to explore the relative search volume, compare it to other keywords, and identify seasonal trends or emerging topics in your industry.
See also: Search volume, Keyword
Further reading: What is Google Trends, and Can I Use it to Find Keywords?