All terms, "ratification" (rtf), "accession" (acs), "approval" (apv) and "acceptance" (acp), signify the consent of a State to be bound by a treaty.
The legal incidents/implications of ratification, accession, approval, and acceptance are the same. The treaty becomes legally binding on the State or the regional economic integration organization.
All the countries that have either ratified, acceded to, approved or accepted the Convention are therefore Parties to it.
Ratification and Accession
The primary (and traditional) distinction is only between ratification and accession. In this regard, it is only States which have signed a treaty, when it was open for signature, that can proceed to ratify it. Signature of itself does not establish consent to be bound, hence the further act of ratification.
States which have not signed a treaty during the time when it is open for signature can only accede to it. Therefore the term "accession".
Acceptance and Approval
The terms "acceptance" and "approval" are of more recent origin and apply under the same conditions as those that apply to ratification. The legal effect is the same as ratification. The uses of these terms have to do with the diversity of legal systems.
Certain countries, specially some East European States use the terms acceptance or approval for purposes of participation in treaties. The terms are also used in cases where organizations rather than States become Parties to an international treaty, for example the EU.
Occurs when one State is replaced by another in the responsibility for the international relations of territory. Generally, a newly independent State which makes a notification of succession is considered a party to a treaty from the date of the succession of States or from the date of entry into force of the treaty, whichever is the later date.