façade is a loan word from French (hence the cédille under the 'c'), and is most commonly written in its unaccented form (facade) in English, which may explain why you couldn't find it in the dictionary.
A facade is the front of a building, but more broadly it can be defined as 'an outward appearance that is maintained to conceal a less pleasant or creditable reality', which is appropriate to the sentence you gave as an example of usage.
A quick google of the text shows that it's written in the context of iOS layers, and it states slightly earlier that a layer's frame is a purely derived property, which is calculated from various properties (bounds size and position). In other words, your 'frame' isn't actually a frame - outwardly it appears as one, but in reality it's simply calculated from the values you provided.