Question

What is the difference between coarse and fine

Answer 1

Sand on a beach is "fine-grained".  Each individual grain is very small.

Glass marbles (of the kind children play with) in a bucket are "coarse-grained".  Each marble is fairly large.

Of course, these are relative terms.  You can have one beach with sand that is finer than the sand at another other beach.  But usually, when we talk about "grain", we're talking about something small enough to fit in your hand, and at the smallest end of the spectrum may be almost microscopic.

In database terms, we often talk about the granularity of data, or of transactions.  Here we're talking about data as if it were marbles or grains of sand.  A coarse-grained transaction is one that affects a fairly large chunk of the database, such as an entire table or hundreds of records.  A fine-grained transaction affects a fairy small chunk of the database, such as a single record or even a single field within a record.