If you see the IP address fe80::0050:8790:4554:2300/16, what does the :: indicate?

The presence of the "::" in the given IPv6 address indicates that there are one or more contiguous blocks of zeros that have been compressed for ease of representation. In IPv6 addressing, "::" can be used only once in an address to replace an extended sequence of zero blocks, simplifying the format. Therefore, the correct interpretation is that the "::" represents one or more groups of consecutive 16-bit blocks of zeros.

To illustrate, if we expand the address fe80::0050:8790:4554:2300, the "::" signifies an entire section of zeros that replaces the sequence of zero blocks within the address. This compression makes it easier to read and write IPv6 addresses.

The other options do not accurately represent the meaning of "::". The subnet mask of 16 indicates the number of bits used for the network portion of the address but does not relate to the "::". A loopback address in IPv6 follows the format "::1", which is distinctly different from the address given. Additionally, while there are private address spaces within IPv6, such as fc00::/7, the address has not been specified or indicated as being private solely based on the "::" notation.