What Does "wind at your back" Mean?  

It is actually quite straight forward.
Imagine walking in a strong wind - if tat wind is coming towards you, it is more difficult to walk, but if it is 'at your back' it is helping you by pushing you along.
Works the same when sailing.

It means exactly that.

For anyone who has ever travelled some long distance on a bicycle, they would know exactly what it means to have the wind in your back instead of in your face.
Riding a bicycle with the wind in your back is a pleasure.
Riding a bicycle with the wind in your face is hell.

Walking with the wind at your back is a lot easier than walking into the wind.

the first person nailed it. If the wind is in front of you, then its pushing you back. You're going to struggle alot, and not get very far. If the wind is at your back, then its pushing you forward, making things easier on you.

Its just a way of saying "may your journey through life not be a hard one."

"Wind at your back", means it's helping you along your way. If you have ever walked into the wind you would know that it makes the trip much more difficult.

Ireland is known to be rainy and I assumed it meant that rather than the wind and rain blowing in your face, it blows at your back. Also wind blowing in your face on a really windy day, slows down your walk. Wind at your back (going in the same direction you are) would make you walk faster. Similar to floating downstream instead of upstream. Hope this helps!

this looks like a blessing of the kind arthur times..

These are all accurate. I would also add that even if the wind is from one side or the other it will tend to blow you off course. If the wind is coming from your front it can work its way in between the openings and chill you more as well.

It means "may the wind always push you forward instead of pushing you back." You wish that someone you love and respect always has the wind at their back because it will help them do what they need to do.

We sang this song when I was in the Glee Club in high school. I sing in the Walker County Christian Chorus and every year at Christmastime, we do The Messiah concert. The title of this song is "Old Irish Blessing" and we sang it as our benediction at the concert we did last Christmas. I have no idea what this line means, myself. It's a pretty song, though, and I had it on my profile page under my avatar for a long time. Maybe some of the other mylotters know.