It means what it looks like - in park gardening language.
it is Trailer Balconia / Naherholung an installation by Eva Ketzer.
Feel free to have a seat, as long as this trailer is parked here. Its flowers are all "carefree plastic", yet inside you find a beginners book about how to plant and grow your flowers.
Last but not least: These real flowers can be found infront of this pink building ensemble, close to a high traffic street in Oberhausen - I like the slight planting dis-order and its resulting color mix.
Am Schloss Oberhausen, Mai 2015 (c) Ebba Jahn