Wikipedia suggests that a Hybrid Bike blends characteristics from more specialised road bikes, touring bikes and mountain bikes. The resulting "hybrid" is a general-purpose bike that can tolerate a wide range of riding conditions and applications.  Many cycle stores will put new riders on hybrids to start their cycling experience and this was certainly the case for Mary and I. We started with Avanti hybrid bikes which had a low entry cost and provided us with a very comfortable ride. 

These type of bikes usually weigh 13 to 16 kg, have a flat bar handlebar, either calliper or disc brakes, and up to 30 gears using a handlebar based gearing system like the Shimano Tiagra 3 x 10 speed below . They also often have mudguards, one or two panniers, a large soft seat, 32 mm tyres, and suspension for the front fork. As you can see in the photo below, Trek, like a lot of bike manufacturers, has converted to using disc brakes.  The flat bars on a hybrid are super comfortable, but they aren’t aerodynamic or fast.

They also often arrive with a kickstand which can be very useful for keeping your bike upright where there are no practical places to park the bike.  Hybrid bikes are easy to ride and are popular with so called 'weekend warriors' who like to join walkers, joggers and riders travelling around popular spots like parks and lakes.