Every couple of weeks someone asks me for a vector file... most times they have no idea what they are asking for or why.
A vector file is usually a file that ends with the extension .eps (encapsulated postscript). Having said that, not all EPS files are vector files. A vector file is made up of editable outlines that define the boundaries of the image or logo. The beauty of a vector file is that it is able to be enlaged infinitely without losing quality.
Conversely, a JPG or TIF file is resolution fixed, meaning that the larger they become, the poorer the quality or reproduction becomes.
If you have a reputable designer working on your behalf then they've given you, or can supply, a vector version of your logo.
If you need a vector version of your logo, give me a shout... I've created vector versions of many client's logos that they can't seem to locate, or never had.