Osaka station is a main station of city of Osaka, prefectural capital of Osaka prefecture. As same as Tokyo station, Osaka station which trains have to end their journeys and reverse out when departing. Actually this type of station is normal in big cities in Japan and terminus type main stations in large cities are just Nagasaki, Niigata and Takamatsu. Which means no city which has more than one million inhabitants have terminus type main station.
There are two things to watch out when using Osaka station. The first thing is that Tokaido and Sanyo Shinkansen do not call at Osaka station. Shinkansen trains call at Shin-Osaka station which is connected with Osaka station by JR Tokaido main line(locally called as JR Kyoto line) and Osaka metro Midosuji line.
The second thing is that only JR calls the station as Osaka station. All other railway operators, Hankyu, Hanshin and Osaka metro include Umeda in their station names, such as Hankyu Umeda, Osaka Umeda and Umeda stations. Therefore if you are heading to hotel located near Osaka station from non-JR station in the region, probably getting off at one of the Umeda stations will be faster and cheaper.