I have a field that should contain the place of a seminar. A seminar can be held:
As a general rule of thumb, in an application, use an enum if:
Use a lookup table if:
Use both if the prior criteria for an enum are met and:
You'll need to pick what you feel is a reasonable cut of for the number of values for your cutoff point, I often hear somewhere between 10 and 15 suggested.
If you are using an enum construct provided by your database engine, the first 2 groups of rules still apply.
In your specific case I'd go with the lookup table.