Marriage vs Wedding

mar·riage noun
1 a (1) : the state of being united to a person of the opposite sex as husband or wife in a consensual and contractual relationship recognized by law (2) : the state of being united to a person of the same sex in a relationship like that of a traditional marriage <same-sex marriage>
b : the mutual relation of married persons : WEDLOCK
c : the institution whereby individuals are joined in a marriage
2 : an act of marrying or the rite by which the married status is effected; especially : the wedding ceremony and attendant festivities or formalities
3 : an intimate or close union <the marriage of painting and poetry — J. T. Shawcross>

wed·ding noun
1 : a marriage ceremony usually with its accompanying festivities : NUPTIALS
2 : an act, process, or instance of joining in close association
3 : a wedding anniversary or its celebration — usually used in combination <a golden wedding>

(according to Merriam-Webster Online Dictionary)

Terlihat bahwa penekanan pada marriage adalah adanya lembaga atau institusi, sedangkan wedding memberi penekanan pada proses awal.
Dalam bahasa Indonesia, marriage sepertinya bisa dipadankan dengan perkawinan dan wedding bisa dipadankan dengan pernikahan. Sebagai contoh, adanya UU Perkawinan bukan UU Pernikahan, karena yang diatur adalah ‘lembaga’-nya bukan semata proses awal saja.