Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

Is the word 'Customizable' a valid English word? Every time I write that word, the spell checker underlines it, and it suggests using 'Customization' or 'Customize'. I'm not a native English speaker, but that word exists in online dictionaries so I wonder why the spell checker underlines it.
The Oxford English Dictionary in its revision of March 2012 defines it as: That may be customized; able to be changed to suit the requirements of the user. Frequently with reference to computer software and hardware. The earliest citation is from 1960. If that definition of customizable suits your purpose, then there's no reason why you shouldn't use it.

I'm wondering which one of these expressions is correct? This stuff or these stuff?.
Stuff is a collective noun it represents a group of objects. Just as one would say 'this group' or 'this pile,' one would say 'this stuff'.

If there are an odd number of competitors at any stage of a single-elimination tournament, one player is excused from play and continues on as if he had defeated his (nonexistent) opponent. This is called 'getting a by'. Or 'getting a bye'. Who knows, maybe it's even 'getting a buy', although I doubt it. My dictionary lists by as meaning 'pass' in card-games, so that suggests that spelling. On the other hand, the image of the referee looking from the single player, to the empty and undefended far side of the field, and then back to the player, shrugging, and saying 'Bye', is too strong to easily discard. Like other parts of the anatomy, everyone's got an opinion. I'm looking for a cite.

Here's what you get: bye 1 |bi| noun 1 the transfer of a competitor directly to the next round of a competition in the absence of an assigned opponent. [From the New Oxford American Dictionary.]