In regards to the Bitcoin network, an overload can occur when the number of transactions on the network reaches a point where miners are not able to confirm them within a reasonable timeframe or when there is too much traffic on the network causing congestion and resulting in longer transaction times and higher fees. An overload can either happen through sudden spikes, such as during periods of excessive market activity or increased usage from BRC20 tokens, or gradual increases in demand that slowly cause delays over time. In summary, an overload occurs when there are more transactions than the system can handle efficiently which ultimately leads to delays and processing issues until mining power catches up with the spike in demand.