I was reading a book where author defined Mindfulness (sati) using these three analogies from different suttas:
The Buddha compares mindfulness to a gatekeeper for a frontier fortress. [Kimsuka Sutta]
There’s another passage where the Buddha says that mindfulness is like a goad. Most of us have gotten away from animal husbandry and farming, and so we don’t even know what a goad is. It’s a long stick with a sharp point. You use it to poke your animals when they’re going the wrong direction, or if they’re standing still when they should be going. The implication here is that the ability to remember what’s skillful and what’s not, and to be able to give yourself a little push or a poke in the right direction: That’s what mindfulness does for you.
And sometimes it’s more than just a little poke.
(May be he is referring to Patoda Sutta. But I'm not very sure because Buddha didn't mentioned Mindfulness in this Sutta. Please provide me correct sutta if there is.)
There’s another passage where the Buddha says that when you see that something unskillful has arisen in your mind, then you act as if your hair were on fire. You do everything you can, as quickly as you can, to put it out. You’re relentless and mindful in being focused on putting out the fire, and nothing else.
And other definitions which is written in Wikipedia:
Mindfulness is the psychological process of purposely bringing one's attention to experiences occurring in the present moment without judgment.
(Authour refers it as equanimity)
But as I understand, I will only call Gate-keeper analogy as Mindfulness. And other analogies falls in the category of Right Effort and Right Resolve.
If we look at MN 117 :
"One makes an effort for the abandoning of wrong resolve & for entering right resolve: This is one's right effort. One is mindful to abandon wrong resolve & to enter & remain in right resolve: This is one's right mindfulness. Thus these three qualities — right view, right effort, & right mindfulness — run & circle around right resolve."
Please correct me if I misunderstood this.