"Presence" shows up everywhere, in yoga class, in leadership training, on the back of a self-help book. It gets used so often that it stops meaning anything specific. Here's a plain, usable description of what it actually points to.
Presence is attention that isn't divided
Most of a normal day is spent partly here and partly somewhere else: replaying a conversation from this morning, rehearsing one for later, half-listening while planning a reply. The body is in one place, and attention is somewhere else entirely.
Presence is what's left when that split closes. Attention and body are in the same place, at the same time. Nothing mystical is required for this description, it's a completely ordinary state that most people experience by accident sometimes: mid-conversation with someone you love, partway up a mountain, in the middle of a task that fully absorbs you.
Why it's rare, if it's so ordinary
The mind's default setting is to run two timelines at once, the past being processed and the future being planned. Full attention on the present moment is a third mode the mind doesn't fall into by default, it has to be trained into it, the same way a muscle gets trained by use.
That's the actual content of a "presence practice": not chasing a special feeling, but repeatedly noticing the split and closing it, until it closes faster and holds longer on its own.
How you'd know it's working
Not by a dramatic shift. By smaller, more reliable signs: conversations that feel more complete, less residue left over from the day, less of that vague feeling of having been "somewhere else" for hours without noticing. Presence, done consistently, changes how ordinary time feels to live through.
This is the whole subject of The Practice of Presence, one technique at a time.