The definition is loose because everyone does it differently, and finds something different.
You should look into Buddhism, or Yoga (which is many many things, only one of which is doing poses on the floor). What most people never understand is that there is a lot of introspection, thinking, reflecting, noticing, altering, and understanding that you should be doing.
One example: by concentrating on your breathing (and I mean really noticing everything about every aspect of the action of taking a breath and what happens before, during, after, etc etc) you will learn things. You will learn how your body works. You will learn what it sounds like when you breathe. You will learn how deep a breath you can take. You will learn how long you can hold it. You will learn how your posture can affect it. You will learn how your breath affects your immediate surrounding. How it can affect your mood. How it can alter sensation. How it can be changed. How it can be tuned. And a million more things, just from spending time thinking about and tinkering with your breathing.
You can take this one concept of constantly noticing, evaluating, and learning about all the possible aspects of one single thing, and begin to do the same thing as you travel, or as you volunteer, or as you do any thing at all.
This is why the concepts of travel, volunteer, etc are so broad. There is an infinite number of possible things to influence your brain, which will alter every possible thing about you (the way you think, talk, speak, act, etc). But you can't just stand in a room and wait for enlightenment. It's an active process. You must seek out change by taking everything in and thinking about it. It doesn't happen overnight.