Safe houses

The Secret Annexe used by the Frank and
Van Pels families along with Fritz Pfeffer

These were houses that people were hidden in when they were trying to escape persecution. Normally they were taken there by someone else who then brought food and other necessary items like; blankets, warm clothing and news from the outside world. If you lived in a safe house then you, normally, had to be very quiet and you couldn't go outside for fear of recognition. If you were hiding in an enemy area and your neighbours realised you were there then they would often call the enemy troops who would then either kill or arrest you.
Some houses were only temporary; somewhere for the refugees to stop for the night on their way out of the country, others were more permanent but they sometimes changed due to the position of enemy forces and conditions.
Food was often in short supply and there was always a risk that you would be discovered. When that happened people would either give themselves up or sometimes, commit suicide. This meant that the enemy wouldn't be able to subject them to torture or gain any information from them.

Link: http://www.historyplace.com/worldwar2/holocaust/timeline.html#top

Sources: http://www.annefrankguide.com/en-gb/content/achterhuis.jpg