Slow is essentially "On Hold".The Developer has given multiple reasons for delays since their first release and we don't know if or when another release will be made.
Aside: I feel we could benefit from something like a "Slow" tag if Abandoned criteria is not being met. This was discussed some time ago in the topic and I still feel it could be helpful for people to understand that a game's development is taking at least 2x longer (as one example multiplier to consider) than a Dev expected.