Signal to Noise Ratio-ADC

Hello to all
I referred some of the IEEE journal, in which the SNR of an ADC is given with dBc and some times dBFs. Please guide me to understand these terminology.
Very thanks in advance.

Added after 1 hours 25 minutes:

Please help in this.

Have you checked wikipedia?
A brief summary:
"Signal-to-noise ratio
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Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering to quantify how much a signal has been corrupted by noise. It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells).

In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is. "Signal-to-noise ratio" is sometimes used informally to refer to the ratio of useful information to false or irrelevant data in a conversation or exchange."
more about the subject here:
https://en.wikipedia.org/wiki/Signal-to-noise_ratio
hth Bob