The most informative moments in order flow are often the ones where a lot happens and the price doesn't change.
Absorption
When heavy taker selling meets a level and price doesn't fall, someone is on the other side taking all of it. Delta plunges, price holds. That's absorption, and it often marks a level that matters. It can also fail: once the buyer stops, the level gives way quickly.
Icebergs
An iceberg order shows only a small part of its full size. On the book you see 1 BTC at a price; on the tape you see 50 BTC trade there. Trades that keep printing at a price while the displayed size barely shrinks suggest that a larger order is hiding behind it.
Imbalance
Order-book imbalance compares the size resting on the bid side with the size on the ask side, close to the mid-price. A strong bid-side tilt can precede small upticks, but the signal is short-lived, and it is sensitive to the spoofing and pulling you met in the last lesson.