But expenses and wages are what is providing the nets!

If you want 100% of the money to be spent on nets, just buy nets yourself, but that isn't enough to provide mosquito nets to the people in foreign countries who need them.

Clearer terms are "overhead" and "programs". Overhead includes salaries, fundraising, marketing, general expenses, etc. Program spend is how much they spend on programs from the stated mission. Providing nets would fall into the latter category.

But I don't want nets, I want people to be helped by nets and that requires a lot of work. So the efficiency of a charity is a way of saying that if you give $10, that means $10*efficiency nets in hands of people that need them.

Although I partially agree with you, it is easy to show why your reasoning doesn't work. Let's say I create a charity to provide nets. I pay myself 99.99% of all donations and use the rest to fly somewhere myself and hand over 10 nets so I get a free vacation as well. And this is not a wholly theoretical discussion, I am sure there has been a charity like this.

Much of the value in such a charity would be getting the nets to the correct people, who are often thousands of miles away from the donor.

Imagine two charities.

One receives money and then pays a 3rd party organization to install mosquito nets. This charity has very low "overhead" in that a huge portion of their income immediately leaves.

One receives money and then pays employees to manufacture and install mosquito nets. Even if this charity installs more nets it'll have higher overhead than the other charity since things like wages are considered overhead.

First, no your statement is not true. You cannot hide expenses in third party companies and suddenly they are not overhead.

Second imagine two companies: - (a) One uses all the extra money on providing nets and delivering them to users in a low cost way so perhaps 0 overhead with the extra contribution. - One uses all the extra money to give it to pay staff, so perhaps 100 overhead for the extra contribution.

Both might be needed, but in general the reason overhead numbers exist is that people are more willing to give when their money goes directly to something they need.

See for example https://www.givewell.org/charities/top-charities

In the first case all of the money is donated. Handing money to people to buy nets would absolutely be counted as programs.

I think that givewell and charity navigator are valuable things. The charity that receives the bulk of my giving is considered highly efficient by both. But I do think that a narrow definition of efficiency does limit certain kinds of charitable organizations.