By default, Excel will display the Chart Element Names when you hover over on chart's different elements, please see the example below:
Please follow the steps below if you want to hide Chart Element Names:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left navigation menu in the dialog box;
Step 4: Uncheck "Show chart element names on hover" under the section of "Chart";
Step 5: Click "OK" at the bottom.