"Activity loss" refers to a situation where someone or something is unable to engage in their usual or planned actions or tasks. It means a decrease or disruption in the normal level of activity or functioning. Full definition
However, you can claim all or a portion of the loss if an exception to the passive activity loss rule applies. (hrblock.com)
The passive activity loss rule, in association with its active participation requirement, is particularly valuable for new investors who may show a loss their first year in the game. (sapling.com)
This is subject to the usual passive - activity loss limitations. (hrblock.com)