Whitespace
Whitespace is the deliberately empty area between and around design elements: margins, line spacing, and the gaps between paragraphs and blocks. It is not wasted space but the means by which related items are grouped, important things stand out, and text becomes readable at all.
In practice
The most common request in SME projects is to pull more content above the fold so that nothing gets missed. The result is usually the opposite: when everything shouts equally, nothing is noticed. Use spacing as a statement, since an offer block with noticeably more room around it reads as more important than one set in a larger typeface. Pay particular attention to the gaps between clickable elements so they can be hit reliably on a phone. When a page feels restless, inconsistent spacing is a more likely cause than the colours.