Snr is a short written form of *senior*, put after a man's name to show that he is the father, when father and son have exactly the same name. If a man called David Chang names his son David Chang too, the father is David Chang Snr and the son is David Chang Jnr (junior). Without it, letters, bank records and news reports could not tell the two apart. You will mostly see it in British and Australian writing, in newspapers, sports reports and family notices. Americans normally write Sr. and Jr. instead. It is only ever written — when you read the sentence aloud, you say the whole word "senior". Some people write it with a full stop, Snr., and some without; both are fine, but be consistent. Note that this is a narrow job: senior has other meanings — older, higher in rank, a final-year student — but as Snr after a name it does one thing only, and only for the father in a same-name pair.