A family of Microsoft word processing software products for creating web, email, and print documents.
What's shown there most probably was applied using the Text Highlight Color tool in the Font group on the Home tab of the Ribbon. Or it may have been applied by including it in a Style applied to the text. What appear to be white lines actually is where the Highlight Color doesn't "take" due to Line Spacing greater than Single - Unlike Paragraph Shading, Highlight Color only applies to the height of the text, itself, not to the space between the lines or between paragraphs.
If a Style was uses you can remove the Highlight Color by modifying the Style to exclude the attribute or by applying a different Style.
Another option is to select the text, click the expander [ ⍌ ] on the Text Highlight Color tool & select No Color. [If the Highlight Color was applied using a Style, though, this method will not modify the Style.]