AEIOU is a method that provides ethnographic researchers with a framework for recording and classifying observations and information about their subject's Activities, Environments, Interactions, Objects, and Users.
AEIOU is Day 2 of 100 Days of UX, an exploratory effort to survey the 100 methods of design outlined in Martin and Hannington's Universal Methods of Design. For 100 consecutive days, I learn one new method a day and write about it.
The aforementioned definition is my interpretation. The formal definition is that AEIOU is an organizational framework reminding the researcher to attend to, document, and code information under a guiding taxonomy of Activities, Environments, Interactions, Objects, and Users.
Activities are the actions people take towards a goal, the paths they follow, and the modes they work in.
Environments are the spaces where the activities take place. Look for what the atmosphere and context are like. How about the spaces? Are they shared or individual? How have the people adapted the environment for their own use, etc?
Interactions are between a person and someone else or thing. Interactions are the building blocks of activities. Look out for people's routines, special interactions between individuals, groups, objects in the environment and across distance and time.
Objects are the building blocks of the environment. Look out for how objects are put to use and how they can take on unexpected uses depending on the context and actions.
Users are the people whose behaviors, preferences, and needs are being observed. Look out for their values, biases, roles, relationships, etc
On a final note, it is important to keep in mind that although AEIOU prescribes categories for observation and coding, these can be expanded and built on depending on the researcher's needs.