| .co.uk is technically a second-level domain, not a TLD. (A number of ccTLDs have subdivisions at the second level like this; for instance .au has .com.au, .org.au, etc.)
Where do .EDU, .GOV, .MIL, and .INT fit in? Like .COM, .NET, and .ORG, they predate the current classifications and ICANN contracts, so they don't fit as well into the current categories. However, since its recent redelegation, .EDU is being operated pretty much like a sponsored, restricted domain (though under the oversight of the US government instead of ICANN, and restricted to US educational institutions), .INT is run directly by the IANA function of ICANN as a highly restricted domain with no separate registry or registrars, and .GOV and .MIL are special cases run directly by the U.S. government. |