Formative testing is usually conducted during website development and is typically used to test a specific feature like the design of a button or the findability of a piece of specific content, etc…
For example: is the user able to find the email form and be able to subscribe to the newsletter? Or is the user able to find a piece of content given the labeling of the button?
Summative testing is conducted at the end of the development, the “Summation” of the development process. Summative testing is used to determine whether a website has successfully accomplished all of its goals.
Qualitative vs. Quantitative Testing
Related to, measuring, or measured by the quantity/quality of something rather than its quality/quantity.