Grid friendly means that an electrical device or system is designed to work well with the electricity grid. The grid is like a big network that carries electricity from where it's made to where it's needed. Just like the roads that cars drive on, the grid has limits on how much electricity it can handle at any one time. If too much electricity is put on the grid, it can cause problems like blackouts or brownouts.
Devices that are grid friendly are designed to use electricity in a way that's helpful to the grid. For example, they might be able to turn themselves off automatically during times when the grid is at its busiest (like during hot summer afternoons when everyone is running their air conditioners) to help prevent blackouts. Or, they might be able to work together in groups to balance out the demand for electricity on the grid, like if a lot of people suddenly turn on their electric cars to charge at the same time.
Being grid friendly is important because it helps make sure that the grid stays reliable and stable. If too many devices are using too much electricity at the same time, it can cause problems. But if devices work together with the grid and share the load, it can help keep the lights on for everyone who uses electricity.