Bradykinesia (brady-, "slow", kinisi, "motion") is characterized by slowness of movement and has been linked to Parkinson's disease and other disorders of the basal ganglia. Rather than being a slowness in initiation (akinesia), bradykinesia describes a slowness in the execution of movement. It is one of the 3 key symptoms of parkinsonism, which are bradykinesia, tremor and rigidity. Bradykinesia is also the cause of what is normally referred to as "stone face" (expressionless face) among those with Parkinson's. A very detailed explanation of this topic can be found at http://www.wemove.org/bradykinesia.
Freezing is characterized by an inability to move muscles in any desired direction.
Rigidity results when there is an increase in muscle tone that causes resistance to passive movement throughout the whole range of motion. There are different types of rigidity. The form just described is the so-called 'lead-pipe' rigidity seen especially in Parkinson's disease. 'Cogwheel' rigidity is a combination of rigidity and tremor which presents as a jerky resistance to passive movement. Spasticity is a special form of rigidity that is present only at the start of passive movement. It is rate dependent and only elicited upon a high speed movement. These various forms of rigidity can be seen in different forms of movement disorders, such as Parkinson's disease.