EARTH aka The RECEPTIVE
This trigram is the symbol of pure yin. It is the half of the whole symbolized by T'ai Chi, and is thus an extreme state that requires to link with it's opposite half, Yang (The trigram called "Heaven" or "The Creative") to restore balance. That said, the overall focus is on integration and so a sense of balance, of symmetry is built-in.
In the I Ching PLUS material, the position of the trigram reflects refinement, alchemical, processes at work such that in the LOWER position of a hexagram this trigram reflects Devotion (to another/others). In the UPPER position of a hexagram this trigrams reflects this devotion doubled to represent Absolute Trust (in another/others). A major point here, that differentiates Earth from Mountain, is the sense of unconditional devotion, whereas in the trigram of Mountain the focus on quality control favours conditions. (also note that the generic nature allows for Yin to represent absolute darkness - see below)
In the IDM template this trigram is representative of contractive blending and thus an overall bias to seeking wholeness. (balance) but through integration. [In the realm of archetypal representations it is more representing of total darkness and also such emotion-based concepts of fear where the blending is to blend-in with the background and so dissapear. In the more typal representations it is more representing the female and the integration with, to recruit and use, social context to assert identity.]
In Chinese Five-Phase theory, Earth is linked to the concept of EARTH and so the concept of FILTRATION but here expressed as filtering based on faith, or a given set of rules (as in species level instincts, religious/philosophical texts etc), as compared the other trigram of filtration, MOUNTAIN, where the filtration is based on personal discernment skills learnt over time.
In the Myers-Briggs/Keirsey systems of persona classification it is linked to XNFP/Advocates and is mostly concerned with identity seeking and thus intagrating inner and outer to become 'one'. (balance) (e.g. Seekers, Enthusiasts, Questors - it is the establishment (or re-establishment) of balance 'inside' that is seeked. This is often done through following of a creed or charismatic individual)
The numeric link is with whole numbers. The Peircean Category is Firstness as Passive/Implicit STIMULUS.