A Comment is text which is intended for readers of source but which is ignored by the compiler. The underlying mechanism of being able to ignore and typically remove comments was important when resources where at a premium, but in modern systems it may be more valuable for commentary to be understood and optionally preserved as code metadata.
Comments tend to exist in either a line-oriented form (where a comment marker indicates the rest of the current line is a comment and therefore the end-of-line provides an implicit terminator) or block form which makes use of an explicit terminator (and can therefore span multiple lines or also be succeeded by code on the same line.
# declares line comments.
/* and */ declare block comments.
// declares line comments. /* and
*/ declare block comments.
/* and */ declare block comments.
/* and */ declare block comments.
/* and */ declare block comments.
# declares line comments.
// declares line comments.
// declares line comments.
<!-- and --> declare block
comments.