# Glossary

This glossary sets out a list of words that refer to specific terminologies, constants, variables or functions in Opus.

<table><thead><tr><th width="193">Term</th><th>Definition</th></tr></thead><tbody><tr><td>Yang</td><td>A collateral type, e.g. ETH, WBTC</td></tr><tr><td>Yin</td><td>The synthetic</td></tr><tr><td>Abbot</td><td>The module that acts as the point-of-entry for end-users to manage their troves.</td></tr><tr><td>Absorber</td><td>A stability pool where users may deposit <code>yin</code> and participate in liquidations, as well as to earn a percentage of debt surplus and additional reward tokens (if any).</td></tr><tr><td>Allocator</td><td>The module that provides a list of recipients of debt surplus, and their percentage allocations, to the Equalizer.</td></tr><tr><td>Base rate</td><td>The interest rate for a given <code>yang</code></td></tr><tr><td>Caretaker</td><td>The module that is responsible for closing down the Shrine and the protocol in a graceful manner, ensuring that the remaining collateral assets are fairly distributed between both trove owners and <code>yin</code> holders.</td></tr><tr><td>Ceiling</td><td>This may refer to:<br>1. Shrine's debt ceiling: Maximum amount of debt allowed for the entire protocol<br>2. A Transmuter's debt ceiling: Maximum amount of debt that can be minted for a Transmuter module</td></tr><tr><td>Controller</td><td>The module that adjusts a global multiplier of interest rates for troves.</td></tr><tr><td>Deposit</td><td>Transferring the underlying collateral asset of a <code>yang</code> to the protocol for a trove</td></tr><tr><td>Enter</td><td>Transferring the underlying collateral asset of a <code>yang</code> from an address to its Gate</td></tr><tr><td>Epoch</td><td>A variable period of time tied to the shares used for internal accounting in the Absorber only.</td></tr><tr><td>Equalizer</td><td>The module that balances the Shrine's budget by either minting debt surpluses or allowing anyone to wipe out debt deficits. It also distributes minted debt surpluses to the recipients from the Allocator module.</td></tr><tr><td>Era</td><td>A variable period of time that spans multiple intervals during which the base rates of all <code>yang</code>s did not change.  </td></tr><tr><td>Exit</td><td>Transferring the underlying collateral asset of a <code>yang</code> from its Gate to an address</td></tr><tr><td>Forge</td><td>Mint <code>yin</code> that is backed by a trove's value</td></tr><tr><td>Gate</td><td>Adapter for the underlying collateral tokens of <code>yang</code>s that holds the deposited amounts</td></tr><tr><td>Interval</td><td>A time step representing a fixed discrete block of time in the Shrine</td></tr><tr><td>LTV</td><td>Loan-to-value ratio</td></tr><tr><td>Melt</td><td>Pay down a trove's debt by burning <code>yin</code></td></tr><tr><td>Provide</td><td>Depositing <code>yin</code> to the Absorber</td></tr><tr><td>Purger</td><td>The liquidation module</td></tr><tr><td>Ray</td><td>Fixed point number with 27 decimal precision</td></tr><tr><td>Remove</td><td>Withdrawing <code>yin</code> from the Absorber, if any remaining.</td></tr><tr><td>Seer</td><td>The oracle module that fetches prices from oracle adapters and submits <code>yang</code>s' prices to the Shrine.</td></tr><tr><td>Sentinel</td><td>A wrapper module over Gates.</td></tr><tr><td>Shrine</td><td>The core accounting module.</td></tr><tr><td>Threshold</td><td>The maximum amount of debt as a percentage of its total value. This may be in reference to a <code>yang</code>, a trove or the Shrine.</td></tr><tr><td>Trove</td><td>A collateralized debt position.</td></tr><tr><td>Wad</td><td>Fixed point number with 18 decimal precision.</td></tr><tr><td>Withdraw</td><td>Withdrawing the underlying collateral asset for a <code>yang</code> from the protocol for a trove</td></tr></tbody></table>

## Disambiguating the different concepts of time

There are three distinct concepts of time that are used in the smart contracts for Opus: interval, era and epoch.

* Interval is a discrete time step of a fixed length of 30 minutes that underpins the Shrine, setting the frequency for price and multiplier updates.&#x20;
* Era is a variable number of intervals where the base rates for `yang`s remain unchanged. Its sole purpose is to facilitate the calculation of the average base rates for `yang`s in the Shrine for a given span of intervals.
* Epoch is a variable period of time that is tied to the "shares" used for internal accounting in the Absorber only. It is used to calculate the amount of `yin`, absorbed assets and rewards that a provider to the Absorber is entitled to withdraw. An epoch is entirely independent of an interval or era.


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