What is this pop-in from the bottom of Chrome for Android? I'm suffering from a pop-in, coming in from the bottom of the screen, in Chrome for Android.

It seems to be doing a Google search with whatever text I may have tapped. There's no button to close, and it's much more of a nuisance than a help.
What is it, and how do I turn it off?
This is Chrome for Android's feature known as Touch to Search.
The user can tap a word to let Google search quickly without leaving the current page.
From Google Chrome Help,

Search the web on Chrome
You can quickly find what you’re looking for on the Internet, in your bookmarks, and in your browsing history.
[...]
Search words on a webpage
You can find more info about a specific word or phrase on a webpage.
Google must be set as your default search engine to use Touch to Search.

On your Android phone or tablet, open the Chrome app.
Open a webpage.
Tap any word on a webpage to highlight it.
Tap on the panel that shows up on the bottom of the page. You’ll see search results for the words you highlighted.

To turn off Touch to Search:

On your Android phone or tablet, open the Chrome app.
Tap More   Settings.
Tap Sync and Google servicesTouch to Search.
Turn off Touch to Search.