Open and distance learning is learning where there is some flexibility, some control in the hands of the learner as to when, where and how (s)he will learn, balanced by structure and support from a provider.

Often abbreviated to ODL, the term is loosely applied to most forms of learning, except for those at the two extremes: classroom-based learning, as at school, where there is little or no flexibility, and self-study and informal learning (qv), which lack any externally-imposed structure or support.

Open and distance learning includes any provision in which a significant element of the management of the provision is at the discretion of the learner, supported and facilitated by the provider.

This ranges from traditional correspondence courses, on-line provision and interactive CD ROMs, to open learning centres and face-to-face provision where a significant element of flexibility, self-study, and learning support, is integral to the provision.

(Taken from the ODL QC Standards)

There is a plethora of designations applied to learning, some of which overlap or are effectively synonymous with ODL; terms like

blended learning.
computer-based learning,
correspondence courses,
distance learning,
distributed learning,
elearning or e-learning,
flexible learning,
home study,
informal learning
mlearning or m-learning,
online learning,
open learning,
personalised learning,
problem based learning (PBL),
resource-based learning,
student centred learning,
web-based learning (WBL),
work-based learning (also known as WBL),
and so on.

There are differences between these terms. But sometimes the subtleties are slight, and serve more to confuse than to clarify.

For some of these differences, and the contexts in which each term is used, see their individual entries.