Okay, kiddo, so there are two countries in Europe called Portugal and Spain. They both love playing something called football, which is like soccer in America. But sometimes they play against each other, and when they do, it becomes a rivalry.
A rivalry is when two groups or teams really want to win against each other. It's almost like a competition to see who is better. This happens a lot in sports and other activities.
The Portugal-Spain football rivalry is a long-standing one, which means it's been going on for a really long time. Both countries have won big tournaments in football, and they both want to be considered the best at it. Sometimes the games between Portugal and Spain get really intense, with players being tough on each other and trying to score lots of points.
But even though they're rivals, both countries actually have a lot in common. They're both located on the Iberian Peninsula in Europe, they both speak a similar language called Portuguese (in Portugal) and Spanish (in Spain), and they both have a deep culture and history.
So, while the rivalry between Portugal and Spain in football can be really exciting and intense, it's important to remember that both countries still share a lot of similarities and respect each other off the field.