Generally whenever you see it the intended meaning is clear and not worth arguing about unless you're actually writing a legal or specifications document or similar.
This is technically incorrect. If you have a board of 9 people, it will result in the wrong rule: It will mean that 6 votes are required for majority instead of the correct 5.
The technically correct definition of majority is "more than half". It's disappointing to see the grandparent stating this correctly downvoted in the gray.
Source: Worked extensively on board and elections procedures for a nonprofit. Also [1] (expand question #4) warns explicitly against using the incorrect "50% plus 1" definition, and clarifies that the definition is "more than half".
50%+1 is only correct about half of the time as the threshold, since votes cast is constrained to integers but not specifically even ones; ⌊50%+1⌋ is correct; as would be >50%, as, instead of trying to impress with (false, for both the 51% and 50%+1 options) precision, would be the both technically accurate and simple “a majority”, or, if the intent to is to emphasize the lack of a higher threshold, “a simple majority”.