What makes a company too big to fail? I have read the too big to fail Wikipedia and as far as I understand, a company is too big to fail (and thus will receive government bail-outs) if it's failure has a significant impact on an important industry or the economy as a whole. Is my understanding correct? For example, a company such as Snapchat would not be bailed out because while it is worth a lot of money, its failure does not hurt the United State's infrastructure or the economy as much as GM's failure.
In economics Too Big To Fail (TBTF) can have slightly different meaning depending on what research you are looking at but generally speaking literature seems to agree that what matters is how interconnected or systemically important firm is (e.g. see Bernanke 2010;  Zhou, 2009).
Systemically important firms are such that other firms critically depend on them. In fact in recent literature you will often see people arguing that TBTF is a misnomer and better terms would be “too complex to fail” or  “too interconnected to fail” (see Kaufman, 2014), because really TBTF has much less to do with actual size than interconnectedness of a firm.
This is the reason why you usually hear the term TBTF being applied to banks or financial institutions. Financial, institutions are an economic equivalent of infrastructure as they help to allocate capital to its most efficient uses and many other firms depend on them (see Mishkin &amp; Eakins Financial Markets and Institutions).
Consequently, whether General Motors or Snapchat are TBTF depends on how interconnected are with the rest of an economy. If there would be significantly many  'influencers' and 'content creators' that they would become significant part of an economy snapchat might be TBTF. This being said although I was not able to find specific papers on examining how interconnected GM or Snapchat are I am going on a limb to say that probably neither of them are TBTF. As argued by Strahan (2013) TBTF in most cases really applies mainly to financial sector due to reasons already mention above.
In fact Strahan specifically argues in that paper that non-financial firms, using General Motors as an example of non-financial firm that would not be TBTF, can only be TBTF in rare cases. Although the paper makes just analytical argument for this and draws only on general literature without actually examining networks of General Motors specifically (importantly note just because firm is bailed out that does not mean it was TBTF - every company has incentive to argue its TBTF to get bailout and policymakers often cannot examine networks in real time so they have to make an educated guesses about whether firm is actually TBTF or not - if a non-financial firm claims to be TBTF its good to be skeptical given literature but I would not dismiss it out of hand either).