The network hashrate is the total computing power that all miners worldwide contribute to a network. Alongside the price, it is the most important figure for miners: if it rises, the same daily payout is spread across more computing power and the yield per device declines - if it falls, the opposite happens. At the same time, hashrate is regarded as a network's security measure, because attacks become more expensive as total power grows.
Difficulty automatically adjusts how hard it is to find a valid block, so the block rate stays constant - it follows the hashrate. Halvings reduce the payout: Bitcoin, Litecoin and Zcash halve the block reward at fixed block heights, Kaspa reduces monthly, Ethereum Classic in five-million-block steps, and Monero pays a constant tail emission. The halving countdown on this page gives an overview of the upcoming dates.
Each coin has its own detail page with the full historical chart of hashrate and difficulty, a price overlay and a halving explanation - for example the Kaspa Network Hashrate page. What the figures mean for a specific device can be calculated in the Mining Calculator.