Qualitative designs are categorial; quantitative are numerical. Yet, they are both rhetorical. In terms of scale, one can adjust the perception of quantitative results, whereas this is much harder to achieve with qualitative designs. Qualitative designs are not mathematical (i.e. you cannot calculate a distance or assign a comparative 'value' to them).
What is the difference between validity and reliability?
The classic example is the dart board. You may be able to produce reliable results (consistent) but are they actually valid for measuring what it is your researching? Result that are valid does not imply reliability (the internal and external consistency of the data), and vise-versa.
What is meant by probability and significance?
These go hand-in-hand. the percent chance of occurrence is the probability, but it may mean little if your data is not significant. You can provide probabilities, means, deviations, etc for objects, but if they are not significantly different, your probabilities are not valid.