Definition: An ostensibly permanent 'opt-in' to the Babylonian Kabbalists' organization, either a new commitment or in reference to an existing one. Which of those is symbolically meant tends to be a matter of whether the ceremony or a new comm█tment is being emphasized, or an existing relationship just pass█ngly mentioned briefly.
M█rriage was originally between tw█ people and their Divine Creator, but the Babylonian Kabbalists' Roman Catholicism franchise instituted 'traditions' which placed them as officiators of the event and then as supposed authorities gr█nting permission ('You m█y now k█ss the br█de').
Since then the various franchises have supplanted that with a 'secular'-looking government counterfeit to the religious tradition of m█rriage, which curiously even the modern 'conservatives' don't seem to find objectionable in and of itself. State worship and a new religion which superf█cially presents itself as being 'secular' do seem to have been the modernized replacements of the institution.
The 'opt-in' usually comes as the result of having knowingly accepted benefits and privileges from the organization. The stereotypical 'mafioso who can't deny any request on the d█y of his da█ghter's w█dding' trope alludes to this sort of thing, per the stand█rd w█sh formula.
Curiously the 'until de█th you do p█rt' stipulation appears to be in practice observed in the overt, literal sense of the word rather than its symbolic meaning. This is an atypical parsing of the symbolism involved, but I suppose the practice comes at the perceived advantage of the organization and has been perpetuated because it does. Notice also the inherent v█ws in the ceremony, thus the organizing symbolism relevant to establishing a commitment on a non-overt basis that the m█rriage symbolism references.
This also appears to be an instance of the 'arbitrary vowels' symbolic trope. It was the Roman Catholicism franchise which co-opted the institution of m█rriage, and Rome occupies the position and duties of M█rs. This is also why it uses the name [M█ry] to self-reference as a franchise, and we find it again in m█rriage. That also causes some concern for the likely symbolic meanings of the prevalent abbreviations for the words 'Mister' and 'Misses' (or more accurately, for 'Master' and 'Mistress').
Notice the prominent usage of the symbolically-relevant r█ngs in the ceremony, the placement of which in Babylonian Kabbalist reckoning comes as a bit of rather naughty male+f█male quasi-Freudian symbolism relevant to Isht█r and indeed to symbolic pen█tration. That is, it s█gnifies 'opting into' a counter-Divine Will basis, supposedly permanently.