Careless driving is defined as operating a vehicle in such a manner as to not provide the proper care and attention to the other users of the roadway.
The charge is based on the totality of the circumstances surrounding the driving, including the attention of the driver to the road, road conditions and whether there has been an accident (although an accident is not necessary for a careless driving charge.
In determining whether the driving is in fact careless, the court has to consider the driving over a period of time and the intention of the driver.
Mere inadvertence to the roadway cannot be held as Careless. If the driver was momentarily distracted, the intent requirement would not be proven.
Careless driving is a Highway Traffic Act offence and does not involve s criminal conviction. There are however significant penalties if you are found guilty.
There is a fine which starts at $300 but can go up to $2,000. It is in the discretion of the judge to impose a suspension of your driving privilege. There are 6 points put on your driving record. For most drivers, this would mean that you are close to or at a probationary period re: maintaining your driver's license.
Also, most insurance companies see this charge as a very serious Highway Traffic Act offence and will likely increase your rates significantly.