That would be "Highlight current word".
If you normally edit the text, then whatever word is at the text-cursor (caret) is highlighted everywhere in the text (after a 1 second wait time).
You can find the settings under Tools > Options > Editor > Color: "Highlight current word"
Simple "uncheck" the colors (foreground/background/...) and it stops.
Also under Tools > Options > Editor > Markup and Matches: you can set the time, and minimum length for full words. But if you select text, it is always the selection.
Maybe there should be options for:
- toggling "highlight current selection"
- disable during search and replace
There are some other ways of renaming stuff.
Refactor "rename identifier"
Source editor, context menu > Refactoring OR menu: Source > Refactoring.
Syncro edit:
https://wiki.freepascal.org/New_IDE_features_since#Syncron-EditSelect the entire procedure, then click the icon in the gutter or use ctrl-j.
Any word that appears more than once, will be in a "box". Editing it in one place will edit all others.