A Weak pulse indicates insufficient activity in that position. The pulse falls well short of feeling vital. The Weak pulse doesn’t have much definition. It results from a deficiency of Qi.
A Weak pulse can result after many other qualities have been experienced; it can be the Yin result of too much Yang having been accumulated. For example, a Wiry pulse which formed due to long-term anger can become so Wiry and consume so much energy that the pulse reaches a point where it cannot sustain the wiry quality and must transform. It flips, leaving it Weak. At that point, the anger transmutes into depression. Suddenly as a result you have Weak pulses with hints that it was once Wiry; it may be Weak with a hint of tightness.
The term Weak can describe a lack of strength at the deep level, especially in the Kidneys as they support the Spleen. Weak can also be used as a relative term to indicate strength when compared with adjacent pulses. When a moderate level pulse disappears as it is pressed to the Yuan level, it can be considered Weak.
Feels like: The Weak pulse gives you the feeling of lack of confidence in that organ or in the fluids of that position.
The Frail or Minute pulse is a subset of the Weak pulse. It feels almost wispy, indicating great Weakness. It is even weaker than the Weak pulse.
Feels like: When pressure is increased, the Frail or Minute pulse disappears.