The Olympus Digital Zuiko 40-150mm f/4-5.6 ED is a budget class tele zoom lens in the Olmypus lens lineup. It is usually sold as part of camera "kits" but it's also available separately for as little as ~200€/US$. Its focal length range is equivalent to about 80-300mm in full format (35mm) terms which should be sufficient for most amateur tele needs. A major feature is its amazingly small size and weight. It's barely bigger than the dwarfish Olympus 14-42mm f/3.5-5.6 ED so it's sometimes hard to distinguish between the two in your lens bag. It's also substantially smaller and lighter than e.g. the comparable Nikkor AF-S 55-200mm f/4.5-5.6 VR (which isn't big either). Just to give you an idea about the size - here's a comparison to the Olympus 50-200mm f/2.8-3.5 ED SWD:

Just like it's kit companion, the 14-42mm, it suffers a bit from its lack of "substance" (in terms of weight/size) but the build quality is actually pretty good. The lens body is all made of light plastic. There's only little friction when zooming throughout the range. As you can see above the lens extends when zooming towards the tele end. The small but usable focus ring is coupled to a focus-by-wire mechanism which is common in many four-thirds lenses. The Zuiko relies on a conventional micro motor for focusing - the AF speed is comparatively slow here. Full time manual focusing is possible in single AF mode.