2f333d6f_UX_Techniques__UX_Mastery___Technique
[What It Is] Asking users to record their experiences and thoughts about a product or task in a journal over a set period of time. [When To Use It] Research [How To Use It] Conducting a diary study is really as simple as providing users with a diary and a timeframe, as well as guidelines about what (and what not) to record. Read Andrew Maier's article, Jumpstart Design Research With A Diary Study for more details. [Technique] 
Diary Study
UX Techniques -UX Mastery 
Technique