Any tool that assists visual presentation and takes up less space than proper sentences. Obvious examples include bullet points, tables or using statements rather than structured sentences. Other examples include using figures rather than words to present numbers or using bold to highlight something rather than adding line breaks. In short, there are many techniques and it depends on the circumstances of each CV in deciding which ones to employ.
Why use them?
Space saving devices are great for controlling the length and layout of your CV. You can use them to fit everything neatly into a full page or dispense with them in order fill space out. They also help presentation. For instance, using tables to present ‘education and qualifications’ helps to keep information in order and look consistent.
Remember: always aim for full pages − half pages don’t look good − and space saving devices are great for using space effectively.