VHF stands for Very High Frequency and is used by most vessels for marine communication.  VHF is used for normal and emergency communication.  

The use of a VHF is regulated in most countries in the EU and a VHF licence is required for operating a VHF radio.  Depending on the country, different regulations may exist for handheld VHF devices.  

Different channels (frequencies) are used for different types of communications, like Ch 16 is used for Distress, safety and calling.  Newer radios, equiped with Digital Selective Call (DSC) will use DSC Ch 70 for this purpose.

VHF typically gives a range of about 20 NM (Nautical Miles) from ship to ship and up to 65 NM from ship to shore.  The actual range depends on the antenna heights involved.  It is therefore important to install your VHF antenna as high as possible.