A trigram is a gram composed of three lines, each of which can be broken (0) or full (1).

The 8 possible trigrams form the basis of the I Ching.

Additional information:

Binary name: 000 - 001 - 010 - 011 - 100 - 101 - 110 - 111
Name used: stone - spark - vortex - flame - pond - volcano - droplet - wind

Meaning:

yin of earth - yang of earth - yin of fire - yang of fire - yin of water - yang of water - yin of air - yang of air
earth of yin - fire of yin - water of yin - air of yin - earth of yang - fire of yang - water of yang - air of yang

Mapping examples:

000 - 001 - 010 - 011 - 100 - 101 - 110 - 111
stone - spark - vortex - flame - pond - volcano - droplet - wind
down - backward - inside - right - left - outside - forward - up
n - ne - w - se - nw - e - sw - s
earth - mountain - water - wind - thunder - fire - swamp - heaven (I Ching elements)
field - bound - gorge - ground - shake - radiance - open - force (I Ching)
receptiveness - arousing - water - openness - stillness - fire - penetrating - creativeness (I Ching)

Traditionally in the I Ching, the lower line represents the realm of earth (material realm), the middle line the human realm, and the upper line the realm of heaven (spiritual realm).

We can also think of the lower line as the microscopic scale, the middle line with the human scale, and the upper line as the macroscopic scale.