This is a holdover from pre-tumblr fandom when (at least for me) there was a degree to shipping.
A couple I ship together doesn’t automatically get the One True Pairing title for me because they have to be a One True Pair-- the ship I ship above all else. Two characters, no matter the circumstance I see will always be right for each other.
Sometimes a ship never rises to OTP levels, but that’s okay, epic love is not the end all and be all. I also love the concept of the love after true love pairings, a concept I owe to The OC.
Then, there’s the golden OTP to end All OTPs, the few OTPairings that rise above all else, in any universe, multiverse they will always be together and mostly these pairings were formed during my formative years: Lois and Clark, Elizabeth and Darcy.
(I still can’t forgive that one show where a Superfan entered the book and ends up with Darcy, also she had more chemistry with Wickham.)