Dictionary.net

One alleging with needless particularity or unnecessary circumstances, what is material and requisite, and which, properly, might have been stated more generally, or without such circumstances or particulars; or, in other words, it, is a statement of unnecessary particulars, in connexion with, and as descriptive of, what is material. Gould on Pl. c. 3, 186.

It is highly improper to introduce immaterial averments, because, when they are made, they must be proved; as, if, a plaintiff declare for rent on a demise which is described as reserving a certain annual rent, payable "by four even and equal quarterly payments," &c.; and on the trial it appears that there was no stipulation with regard to the time or times of payment of the rents, the plaintiff cannot recover. The averment as to the time, though it need not have been made, yet it must be proved, and the plaintiff having failed in this, he cannot recover; as there is a variance between the contract declared upon and the contract proved. Dougl. 665.

But when the immaterial averment is such that it may be struck out of the declaration, without striking out at the same time the cause of action, and when there is no variance between the contract as, laid in the declaration and that proved, immaterial averments then need not be proved. Gould on Pl. C. 3, 188.