The Church of Jesus Christ of Latter-day Saints has a three-year system for collecting and spending tithes.
In the first year the funds are collected.
In the second year the funds remain invested while a budget is prepared for spending the tithing.
In the third year the funds are spent.
During the time when the funds are collected (first year), they are put to use in investments or deposits which yield a return. Similarly, while they remain invested during the second year, they also yield a return. When the third year arrives, and the funds are being spent on budgeted expenses, until the day they are spent they continue to collect interest or a return.
The amount of tithing collected in the first year is the amount designated “tithing” contributions. This is the amount that is budgeted and spent in the third year. All of the return on tithing yielded in the form of interest or return on investments is treated as “investment income” not tithing.
When the church spends “tithing” on temples, chapels, publications, etc. those monies are confined to the original amount collected as “tithing” only.
When the church spends “investment money” those include the interest, return, etc. collected on the tithing money during the three year cycle from when originally collected until the time it is spent. It also includes the returns on the returns as they accumulate over the years.
Therefore, when the church announces that a project (like the large reconstruction of downtown Salt Lake City) is not “tithing” but is “investment income” of the church, this is the distinction which is being made.