Short Desc: Free tool from Google that allows you to see general search trends at various time frames.
URL: https://trends.google.com/trends/?geo=US
The most common uses of Google Trends data will be during Marketing Assessment and working on SEO Research when building out your SEO content optimization strategy.
Google Trends allows you to take a quick graphical fluctuation at Google Search Trends at various time periods with the shortest time period being 1-hour and the longest time period being 2004-present.
For Marketing Assessment and SEO Research purposes, the most common trends you will be researching are 1-year and 5-year trends
For example, in the below screenshot for "Google Ads" and "Google AdWords", the 12-month screenshot shows volume is mostly steady throughout the last year except for a substantial surge during the holiday season.

While the 1-year graph tells a story, it does not tell the entire story. Below is the graph from the exact same keywords the only change being taking a look at the 5-year trend. From this what you can see is that "Google Ads" search volume has moved up while "Google AdWords" has trended down substantially - not surprising as Google did a rebrand from "Google AdWords" to "Google Ads" that is consistent with the below trend.

A couple other things to keep in account if you see skewed data:

3. Google Trends will default to the 12-month view, to shift to the 5-year view, click the dropdown next to where it says "Past 12 Months"

4. Select "Past 5 Years"

Unresolved questions you are still working through and need feedback on.