All lawns will seed, it's the natural means by which it propagates itself into a new generation. The seeding can be very different in all lawn types. For example, Buffaloes will produce a thick, heavy seed stalk and head, Kikuyu seeds are so fine, you need to look hard to see them, and Couch seeds can be fine, easily seen, and produce in abundance.
Chances are, if you have a newer lawn variety it will may be a hybrid. What this means is that the lawn plant and it's seeds are both sterile, for this reason, the seeds cannot propagate a new lawn. The only means of propagating or starting a new lawn with Hybrid varieties is to plant runners from a parent lawn. Lawn types such as Buffalo have always been notoriously difficult to propogate from seed, and this is why Buffalo must be started from either grass runners or roll on lawn.
In some lawns, and most noticeably in the Couch varieties, heavy seeding can occur in an abundance and very quickly.
Lawns will do this when it enters into a state of shock, something in it's environment or lawn care has changed, and the survival mechanisms of the plant have activated. Instead of using its energy for it own health and growth, the lawn believes it is about to die, and uses all of its energy to produce as many seeds as possible to ensure the survival of the species if it were to die.
So what happened?
The answer can be any number of factors, lack of water, sudden drop in watering amounts or frequencies, lack of nutrients, or a sudden increase in temperature. Anything which may cause stress in lawns can be a cause for grass to go to seed. Many lawn types may also just be highly succeptible to seeding, and these factors are covered in other articles throught The Lawn Guide.
The simple solution is to mow the lawn and remove the seed heads, put down a quality lawn fertiliser in the amounts listed on the product packaging (and no more), followed by a good watering in of the lawn fertiliser.
Follow this up with a few good deep waterings over the next couple of weeks, and the problem should be rectified. It can be a good idea to figure out what the original cause was and rectify that as well, if possible, and begin a quality lawn care regime.
Highly respected Australian turf and plant breeder Todd Layt shares expert lawn care advice with homeowners on The Lawn Guide.