Spiritual gobbledygook? No!
In my first (and so far only) Mahamudra meditation retreat, one of the instructions for a particular meditation practice was this:
"Now begin sealing with respect to immediacy...Moment by moment by moment, recognizing each event by the head, right when the event begins to occur, not after it is already elaborated, nail the event at the head, quick, quick, quick... .."
Sealing and nailing in Mahamudra meditation
The above quote is a meditation instruction in the style of Mahamudra style "pointing out instructions" on how to "nail", or "seal", ie to become aware of mental events at the moment they arise, and to recognize them as mental constructs and fabrications.
A mental event may be a sensation, an emotion, or a thought. The instruction guides the meditator towards recognizing (becoming aware of) all feelings, thoughts and sensations at the moment of their initial appearance. They should be caught before they unfold as a concept, a thought, a story etc.
At this moment, they are said to be recognized as "empty" (see below), and sealed or nailed. Once this happens, they "arise as empty".
"Seal it with the imprint of true nature" (Daniel P Brown)
The following diagram shows how Buddhist thinkers describe the unfolding or spreading of thoughts from the subtle level to the coarse level.
"Sealing" and "nailing" are synonyms. Another term is "hitting" (Guinness 2018). All terms express the activity of conscious processing as "recognising" mental movement the moment it begins.
Sealing
Metaphorically, sealing in Mahamudra meditation is a kind of labelling or stamping a mental event with the "seal of awareness ". As an event (such as an arising thought) is sealed, its identity as a mental fabrication is recognised and stamped on it forever. This way, it loses its power over the mind, as it dissolves under the light of awareness.
A fundamental work of Mahamudra has therefore the title "The Royal Seal of Mahamudra".
Nailing
Nailing is related to the English expression "he nailed it", meaning that she understood it precisely. Or, in "she hit the nail on the head". That's why nailing may also be translated as "hitting".
The term "to nail" in Tibetan has a similar meaning to the word to nail as it is used in colloquial English. When a gymnast does a perfect routine, we say that he or she "nailed" the routine. Similarly, when an advanced yogi or yogini penetrates the essential points of a set of pith instructions and comes to the full realization, a Tibetan would say that the yogi or yogini "nailed" the realization (Tapihritsa et al., 2022, p. 3)
Here is even a book on nailing, with 21 nails of wisdom:
Sealing and nailing have two dimensions in which they operate: immediacy and range.
Speed: Immediacy of sealing/nailing
Immediacy is about timing.
The immediacy of sealing or nailing is the speed with which the meditator recognizes any event as soon as it arises from the subtle domain of unelaborated mind moments. The earlier the recognition happens in the chain of unfolding, the higher the speed.
Daniel P Brown taught "the four levels of nailing" (from notes of Level 1 retreat) . This concept is related to the above mentioned "lifecycle" of events.
Level 1: a mental event (eg a thought) is recognized after the fact. This corresponds, he says, to the Ocean and Wave practice. A wave is recognized when it has already developed
Level 2: the meditator has trained themselves to intentionally recognise events as soon as they arise
Level 3: the process in (2) is now so well trained, that it is effortless and automatic.
Level 4: this "primordial" recognition happens outside of time, and I must that I cannot explain it in the absence of my primary experience.
The higher the "immediacy" , the less conceptualized meditation will be. That's because subtle movements of the mind have no opportunity to spread and develop into conceptual constructs.
So, for the meditator who has reached a certain stage, their main task is to speed up recognition:
if everything's non-dual there's nothing else you need to do other than increase the speed of recognition of each and every event. So it's all about the speed or immediacy of recognition. (Diperna 2022.09.14, n.d.)
The immediacy is also expressed in the metaphor of catching the snake (of thought) at its head. See here.
Scope: Range of sealing/nailing
The range of sealing/nailing is about the scope of mental events which are captured.
For example, the meditator may be well aware of any arising emotion, or everyday thought.
However, she may not become aware of a very seductive and hard-to-recognize type of thought: namely, thoughts about meditation activity and meditation strategy.
For example, such thoughts could be "am I doing this right?", "oh, this is it!", "is my view correct?" and others.
It can also be limiting beliefs, fears, striving for outcomes, fears of not making it, being too slow, judgements, subtle effort etc.
Here a few more unsystematized categories of mental events :
Moods
Beliefs
Limiting Beliefs
Emotions / Feelings
Judgements
Expectations
Intentions / Goals
Perceptions / Sensations
Memories
Images
Thoughts