The most requested terms
All relevant tourism related concepts are presented and explained below

Accommodation
Accommodation can be private and collective, whereas collective is divided to registered (hotels and similar establishments (guest houses), youth hostels, holiday villages and camping sites) and non-registered (short-stay accommodation offered via collaborative economy platforms) accommodation establishments.
An accommodation establishment is an establishment providing overnight lodging for travellers in rooms or some other units.

Visitor
A visitor is any person travelling to a place other than his/her usual environment and staying there for no longer than three (3) months and whose main purpose of travel is not continuous or other than the exercise of an activity remunerated from within the place visited. The term visitor (domestic and foreign) comprises overnight and daily visitors.

Visitor spending
Visitor spending refers to the total consumption expenditure made by a visitor, or on behalf of a visitor for goods and services during his/her trip to the destination. It also includes payments in advance or after the trip for services received during the trip.
Concepts
Arrivals to accommodation
In tourism statistics, an "arrival" is a statistical unit used to measure the volume of tourist/visitor flows. In accommodation statistics, arrivals refer to guest arrivals in accommodation establishments who check in to spend one or more nights in the establishment. 'Arrivals' also indicate the demand for accommodation services measured by the number of customers.
Bed nights
Bed nights refer to the total number of nights spent in accommodation establishments. Bed nights are calculated by arrivals to accommodation*length of stay.
Daily visitors
Daily visitor refers to same-day visit made in the purpose of travel. The maximum duration for same-day visits is less than 24 hours, so that departure and return takes place within the same calendar day and no nights are spent during the trip.
Movement data
Movement data is mobile operator data, which in Finland is produced by ELISA and in Sweden by Telia. Movement data estimates visitor flows based on length of stay on a measuring point and based on the origin of the mobile (county level).
Overnight visitor
Overnight visitor refers to a trip outside the usual environment, during which at least one night is spent in private or collective accommodation either for free or for a charge. The maximum duration of a trip is three months.
Visitor spending
Visitor spending refers to the total consumption expenditure made by a visitor, or on behalf of a visitor for goods and services during his/her trip to the destination. It also includes payments in advance or after the trip for services received during the trip. Visitor spending includes VAT. The figures are estimates and based on the results of the TAK Border Research, TAK Domestic Tourism Survey and accommodation statistics of Statistics Finland. Coefficients of the number of daily visitors and overnight visitors are calculated on a regional level monthly. The coefficients are: [the number of overnight visitors/the number of overnight visitors in hotels, hostels and camping] and [the number of daily visitors/the number of overnight visitors]. The coefficients of spending are calculated on a regional level yearly. The coefficients here are [the average spending of daily visitors] and [the average spending of overnight visitors].
Visitor
A visitor is any person travelling to a place other than his/her usual environment and staying there for no longer than three (3) months (note by UNWTO 12 months) and whose main purpose of travel is not continuous or other than the exercise of an activity remunerated from within the place visited. The term visitor (domestic and foreign) comprises overnight and daily visitors.
*Regional economic effects of tourism
A few basic concepts are applied in regional economic studies of tourism. These include direct, indirect and derivative effects. Tourism brings new money from outside the region to the regional economy and its circulation. Tourists spend money in the destination area on various services, such as accommodation, catering, transport and program services, as well as retail and service station operations. When they directly buy goods and services from companies, there are immediate effects. Indirect effects occur when companies that receive direct tourism income purchase goods and services from supplier companies. These procurement chains can be several rounds in length. Thanks to tourism, when employed people buy goods and services, induced effects are created. All of the effects mentioned above concern tourism income and jobs, as well as wage income and tax income effects accumulated from jobs. Indirect and derived effects form the multiplier effects of tourism. The overall effects of tourism include direct, indirect and derived effects.
Sources
Statistics Finland, TAK Research, Eurostat, Kauppila (2009)