An electric bike is a bicycle that, in addition to normal cycling, offers additional electrical assistance when pedalling. The motor and battery ensure that this support is generated and transmitted. This makes cycling on an electric bike not only faster, but also more comfortable. You have to make less effort to pedal than with a normal bicycle.
Among electric bikes, you also have the newer and even faster variant, the speed pedelec. The speed pedelec is a fast electric bicycle that can reach a much higher speed. For example, a speed pedelec supports up to 45 km/h instead of the 25 km/h of a regular e-bike.
All these terms are used interchangeably, which may cause some confusion. Actually, everyone uses the terms electric bike and e-bike interchangeably. There are also different spellings: ebike, e bike and e-bike. E-bikes are simply a synonym for electric bicycles. The term e-bike is of course a bit shorter to write! Don't worry about these different names: everyone understands what you are talking about when you talk about an e-bike or electric bicycle.