In our world, it's not a heart attack (thank goodness), a stroke is the Photoshop industry term for an "outline" or "border".  You can add a stroke to a layer from the blending option/layer effects panel by right-clicking on the layer in the palette or by clicking on the lower left icon in the layer's palette and choosing stroke.

A Stroke will put an outline around your text or other layer.  You can choose and change the color and like other layer effects, the distance, size and opacity of the effect.  You can even change the blending mode (but in most cases that won't make a difference).  Strokes are used all the time in flyer's and advertisements.  They work great to help isolate text from a busy background. 

In most cases you'll use a size of 3 or less but when you start enlarging or working at a higher resolution (700) you may have to enlarge the size of the stroke when previewing it at print size.  Stroke works well only with clear cut lines or edges (ie. text or shapes).  You can stroke a layer of a person as long as it is a good selection but sometimes outer glow will work better so you don't see the harshness of an imperfect selection which will show through with a stroke.  Here is an example where you can see the stroke effect.

Stroke also works best on chunky text vs. cursive text.  As with all layers you can lower the opacity to dim the entire layer and its effects or you can lower the fill to only retain the layer effects you have applied (in this case, the stroke).  Here you can see the nice white 'stroke' of 1 pixel as a layer style/effect on the text and a red stroke on the bottom image.

There is another way to create a stroke and that is by duplicating a (text) layer, rasterizing it and expanding it (by 1-4 pixels) and filling it with a color while leaving the original layer (usually white) in front.  You can then link them or merge them.  I show how this is done in the Discover Photoshop: Total Package training program.  But it's simply easier to use the layer effect: stroke from right clicking on the layer.  Many times there are several different ways to do things in Photoshop. 

This effect is used throughout many genres of design and should be aware of it and how to use it.  Stroke it to the west, baby.

- Article by Orion Williams copyright 2004

Remember: saving for web automatically flattens all the layers in the image at the time you export it.