Parenthesis and parentheses
Solution 1:
Most people confuse Paranthesis to be "(" or ")" or "(...)". When in actual the parenthesis is any amplifying or explanatory word, phrase, or sentence that’s set off from a sentence or passage by some form of punctuation.
It can be a pair of enclosing commas, a pair of enclosing dashes or parentheses.
Here are few examples:
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Parenthesis by comma: “Ferdinand Magellan, who claimed the Philippine islands for the Spanish crown in 1521, was actually a Portuguese whose native name was Fernão Magalhães.”
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Parenthesis by dashes: “Their kindly uncle was terminally ill—they said they didn’t know it then—but his nephews and nieces just went on their merry ways.”
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Parenthesis by parentheses: “While I was driving it out of the used-car dealer’s yard, the nicely refurbished 1994 sedan (the dealer assured me its engine had just been overhauled) busted one of its pistons.”
Read this blog for further details.
Parentheses means a pair of "(" and ")". Hence in your example, one would say "abc is inside the parentheses".
In modern days, people use paranthesis as any one of "(" or ")" which is widely accepted.