It is a mastic stamp in English - a stamp with a specific design as emblem that serves as a registration/ application mark.
The following is a similar sample of a mastic stamp used in Moscow although it is not for visa specific purposes. But it will give you a better idea of we are talking about:
http://www.ggk.mos.ru/eng/documentation/

As opposed to "machine-readable stamp/form" ("визовый бланк")

Форма и порядок заполнения машиночитаемого визового бланка, вклеиваемого в паспорт

1. Машиночитаемый визовый бланк, изготавливаемый в соответствии с рекомендованным ИКАО международным стандартом (Doc 9303, часть 2), представляет собой талон размером 120 х 80 мм с нанесенным на его обратную сторону самоклеющимся слоем. Заполненный машиночитаемый визовый бланк отделяется от бумажной подложки и вклеивается в паспорт.
2. При оформлении визы на машиночитаемом визовом бланке в него вносятся следующие сведения:
1) однократная, двукратная или многократная виза;
2) дата выдачи визы;
3) гражданство владельца паспорта;
4) даты начала и окончания действия визы;
5) срок пребывания;
6) трехразрядный буквенно-цифровой код - категория и вид визы:
http://www.advokats.ru/index-ea=1&ln=1&map=1&chp=showpage&pa...



The visa is an ink stamp on one of the pages of your passport and a form pasted in your passport.
http://www.crummer.rollins.edu/international/obtain_visa.sht...

Entry Visa: A machine-readable stamp in your passport issued by an American Consulate abroad, authorizing you to apply for admission to the United States at the port of entry
http://www.cobleskill.edu/international_immigrationDefinitio...

On entry and exit, third country nationals are subject to thorough checks which comprise a verification of the conditions governing entry and, if applicable, of documents authorising residence and the pursuit of a professional activity.

For stays not exceeding three months per six-month period, third-country nationals must:

possess a valid travel document;
possess a valid visa, if required;
justify the purpose of their intended stay, and have sufficient means of subsistence;
not be a person for whom an alert has been issued in the SIS for the purposes of refusing entry;
not be considered a threat to public policy, internal security, public health or the international relations of the Member States.
If these conditions are not met, entry to the territory may be refused, unless the special provisions concerning the right of asylum and other humanitarian reasons apply.

The travel documents of third-country nationals are systematically stamped on entry and exit. If a travel document does not bear an entry stamp, it may be presumed that the holder does not fulfil, or no longer fulfils, the conditions of stay. The third-country national may however provide, by any means, credible evidence, such as transport tickets or proof of his or her presence outside the territory of the Member States, that he or she has respected the conditions relating to the duration of a short stay. From: http://europa.eu/scadplus/leg/en/lvb/l14514.htm

It's called Border Control, the place where they put these stamps into your passport. There can also be a stamp in your passport (i got one in mine, in Holland) issued by the DEepartment of Immigration (or whatever), in essence allowing you to stay in the country fro a longer period of time than the normal entry stamp of three months, and bearing with it a permission to excercise some rights.