ETYM . semi-colon.
A punctuation mark (;) used to connect independent clauses; indicates a closer relation than does a period.
Punctuation mark (;) with a function halfway between the separation of sentence from sentence by means of a period, or full stop, and the gentler separation provided by a comma. It also helps separate items in a complex list: “pens, pencils, and paper; staples, such as rice and beans; tools, various; and rope”.
Rather than the abrupt “We saw Mark last night. It was good to see him again”, and the casual (and often condemned) “We saw Mark last night, it was good to see him again”, the semicolon reflects a link in a two-part statement and is considered good style: We saw Mark last night; it was good to see him again. In such cases an alternative is to use a comma followed by and or but.