It is a number-pattern clue.
The acronym of the clue is the wifi password at the home of the family for whom Clara works as a nanny.
The expression form of the clue is a combination of the things she has said before each of the three times she has died :
Run You Clever Boy And Remember 1 2 ?
The “?” indicates that the video was cut right at the precise moment the actor was about to say the third number. We never heard the third number; we assume Clara heard it just fine because she entered it into the computer, in plain text so we could see it:
Notice the 4 where you would expect a 3, it being the simplest number pattern which is easy to remember: a common memory trick for a password.
Later, in her journal, The Doctor found a page where she had written her age down every year without fail since she was 8. Except she skipped a year at the end, and ended the vertical column of numbers with: “21 23 24”. The key to this for me, weak in the “detecting patterns in numbers” exercise (I suck at those: “what are the next numbers in a sequence” tests), I noticed that written vertically, my eye was distracted by the symmetry of the “2” in the tens column, which when ignored revealed another pattern: “1 2 4”.
Clara missed the year 23, and this clue presented itself twice in the movie: once in her recollection, and once in his.
One of the forms of the clue instructs him to de-ass the area and get to when she is 23, and find out why she is missing that year.