medium
The Italian word 'medio' is used in a similar way to the English word 'medium'. It can refer to a size, such as a 'medium' pizza, or a level of something, such as a 'medium' difficulty. It can also refer to something that is average or in the middle. For example, 'un prezzo medio' means 'an average price'. In a mathematical context, 'medio' can also mean 'mean' or 'average'.
The middle class in Italy is disappearing.
This sentence talks about the socio-economic trend in Italy where the middle class—people who are neither very rich nor very poor—is allegedly getting smaller.
In the Middle Ages, life was very different.
This sentence refers to a historical period, the Middle Ages. The speaker is making a comparison between life during that time and life today.
The middle point of the bridge is the safest.
The speaker is saying that the center of the bridge is the safest place—perhaps because it's usually the sturdiest part, furthest away from the edges.